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| <label for=m-zh-cndocsv27userexamplesparameter-validation-check><a href=/zh-cn/docsv2.7/user/examples/parameter-validation/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesparameter-validation><span>参数验证</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesgeneric-invoke-with-json-li><input type=checkbox id=m-zh-cndocsv27userexamplesgeneric-invoke-with-json-check> |
| <label for=m-zh-cndocsv27userexamplesgeneric-invoke-with-json-check><a href=/zh-cn/docsv2.7/user/examples/generic-invoke-with-json/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesgeneric-invoke-with-json><span>JSON泛化调用</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesmsgpack-serialization-li><input type=checkbox id=m-zh-cndocsv27userexamplesmsgpack-serialization-check> |
| <label for=m-zh-cndocsv27userexamplesmsgpack-serialization-check><a href=/zh-cn/docsv2.7/user/examples/msgpack-serialization/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesmsgpack-serialization><span>msgpack序列化</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesprovider-timeout-release-li><input type=checkbox id=m-zh-cndocsv27userexamplesprovider-timeout-release-check> |
| <label for=m-zh-cndocsv27userexamplesprovider-timeout-release-check><a href=/zh-cn/docsv2.7/user/examples/provider-timeout-release/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesprovider-timeout-release><span>provider超时打断</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesresult-cache-li><input type=checkbox id=m-zh-cndocsv27userexamplesresult-cache-check> |
| <label for=m-zh-cndocsv27userexamplesresult-cache-check><a href=/zh-cn/docsv2.7/user/examples/result-cache/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesresult-cache><span>结果缓存</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesbroadcast-resp-collect-li><input type=checkbox id=m-zh-cndocsv27userexamplesbroadcast-resp-collect-check> |
| <label for=m-zh-cndocsv27userexamplesbroadcast-resp-collect-check><a href=/zh-cn/docsv2.7/user/examples/broadcast-resp-collect/ title=收集Dubbo广播响应 class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesbroadcast-resp-collect><span>收集广播响应</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesinvoke-with-specified-ip-li><input type=checkbox id=m-zh-cndocsv27userexamplesinvoke-with-specified-ip-check> |
| <label for=m-zh-cndocsv27userexamplesinvoke-with-specified-ip-check><a href=/zh-cn/docsv2.7/user/examples/invoke-with-specified-ip/ title="指定Ip Port调用Provider" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesinvoke-with-specified-ip><span>指定IP</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesgeneric-reference-li><input type=checkbox id=m-zh-cndocsv27userexamplesgeneric-reference-check> |
| <label for=m-zh-cndocsv27userexamplesgeneric-reference-check><a href=/zh-cn/docsv2.7/user/examples/generic-reference/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesgeneric-reference><span>使用泛化调用</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesprotobuf-idl-li><input type=checkbox id=m-zh-cndocsv27userexamplesprotobuf-idl-check> |
| <label for=m-zh-cndocsv27userexamplesprotobuf-idl-check><a href=/zh-cn/docsv2.7/user/examples/protobuf-idl/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesprotobuf-idl><span>Protobuf</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplespb-generic-reference-li><input type=checkbox id=m-zh-cndocsv27userexamplespb-generic-reference-check> |
| <label for=m-zh-cndocsv27userexamplespb-generic-reference-check><a href=/zh-cn/docsv2.7/user/examples/pb-generic-reference/ title="GoogleProtobuf 对象泛化调用" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplespb-generic-reference><span>Protobuf 泛化调用</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesgeneric-service-li><input type=checkbox id=m-zh-cndocsv27userexamplesgeneric-service-check> |
| <label for=m-zh-cndocsv27userexamplesgeneric-service-check><a href=/zh-cn/docsv2.7/user/examples/generic-service/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesgeneric-service><span>实现泛化调用</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesecho-service-li><input type=checkbox id=m-zh-cndocsv27userexamplesecho-service-check> |
| <label for=m-zh-cndocsv27userexamplesecho-service-check><a href=/zh-cn/docsv2.7/user/examples/echo-service/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesecho-service><span>回声测试</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplescontext-li><input type=checkbox id=m-zh-cndocsv27userexamplescontext-check> |
| <label for=m-zh-cndocsv27userexamplescontext-check><a href=/zh-cn/docsv2.7/user/examples/context/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplescontext><span>上下文信息</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesattachment-li><input type=checkbox id=m-zh-cndocsv27userexamplesattachment-check> |
| <label for=m-zh-cndocsv27userexamplesattachment-check><a href=/zh-cn/docsv2.7/user/examples/attachment/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesattachment><span>隐式参数</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesasync-call-li><input type=checkbox id=m-zh-cndocsv27userexamplesasync-call-check> |
| <label for=m-zh-cndocsv27userexamplesasync-call-check><a href=/zh-cn/docsv2.7/user/examples/async-call/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesasync-call><span>异步调用</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesasync-execute-on-provider-li><input type=checkbox id=m-zh-cndocsv27userexamplesasync-execute-on-provider-check> |
| <label for=m-zh-cndocsv27userexamplesasync-execute-on-provider-check><a href=/zh-cn/docsv2.7/user/examples/async-execute-on-provider/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesasync-execute-on-provider><span>异步执行</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexampleslocal-call-li><input type=checkbox id=m-zh-cndocsv27userexampleslocal-call-check> |
| <label for=m-zh-cndocsv27userexampleslocal-call-check><a href=/zh-cn/docsv2.7/user/examples/local-call/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexampleslocal-call><span>本地调用</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplescallback-parameter-li><input type=checkbox id=m-zh-cndocsv27userexamplescallback-parameter-check> |
| <label for=m-zh-cndocsv27userexamplescallback-parameter-check><a href=/zh-cn/docsv2.7/user/examples/callback-parameter/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplescallback-parameter><span>参数回调</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesevents-notify-li><input type=checkbox id=m-zh-cndocsv27userexamplesevents-notify-check> |
| <label for=m-zh-cndocsv27userexamplesevents-notify-check><a href=/zh-cn/docsv2.7/user/examples/events-notify/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesevents-notify><span>事件通知</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexampleslocal-stub-li><input type=checkbox id=m-zh-cndocsv27userexampleslocal-stub-check> |
| <label for=m-zh-cndocsv27userexampleslocal-stub-check><a href=/zh-cn/docsv2.7/user/examples/local-stub/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexampleslocal-stub><span>本地存根</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexampleslocal-mock-li><input type=checkbox id=m-zh-cndocsv27userexampleslocal-mock-check> |
| <label for=m-zh-cndocsv27userexampleslocal-mock-check><a href=/zh-cn/docsv2.7/user/examples/local-mock/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexampleslocal-mock><span>本地伪装</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesdelay-publish-li><input type=checkbox id=m-zh-cndocsv27userexamplesdelay-publish-check> |
| <label for=m-zh-cndocsv27userexamplesdelay-publish-check><a href=/zh-cn/docsv2.7/user/examples/delay-publish/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesdelay-publish><span>延迟暴露</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesconcurrency-control-li><input type=checkbox id=m-zh-cndocsv27userexamplesconcurrency-control-check> |
| <label for=m-zh-cndocsv27userexamplesconcurrency-control-check><a href=/zh-cn/docsv2.7/user/examples/concurrency-control/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesconcurrency-control><span>并发控制</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesconfig-connections-li><input type=checkbox id=m-zh-cndocsv27userexamplesconfig-connections-check> |
| <label for=m-zh-cndocsv27userexamplesconfig-connections-check><a href=/zh-cn/docsv2.7/user/examples/config-connections/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesconfig-connections><span>连接控制</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexampleslazy-connect-li><input type=checkbox id=m-zh-cndocsv27userexampleslazy-connect-check> |
| <label for=m-zh-cndocsv27userexampleslazy-connect-check><a href=/zh-cn/docsv2.7/user/examples/lazy-connect/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexampleslazy-connect><span>延迟连接</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesstickiness-li><input type=checkbox id=m-zh-cndocsv27userexamplesstickiness-check> |
| <label for=m-zh-cndocsv27userexamplesstickiness-check><a href=/zh-cn/docsv2.7/user/examples/stickiness/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesstickiness><span>粘滞连接</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplestls-li><input type=checkbox id=m-zh-cndocsv27userexamplestls-check> |
| <label for=m-zh-cndocsv27userexamplestls-check><a href=/zh-cn/docsv2.7/user/examples/tls/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplestls><span>TLS</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplestoken-authorization-li><input type=checkbox id=m-zh-cndocsv27userexamplestoken-authorization-check> |
| <label for=m-zh-cndocsv27userexamplestoken-authorization-check><a href=/zh-cn/docsv2.7/user/examples/token-authorization/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplestoken-authorization><span>令牌验证</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesrouting-rule-li><input type=checkbox id=m-zh-cndocsv27userexamplesrouting-rule-check> |
| <label for=m-zh-cndocsv27userexamplesrouting-rule-check><a href=/zh-cn/docsv2.7/user/examples/routing-rule/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesrouting-rule><span>路由规则</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesrouting-rule-deprecated-li><input type=checkbox id=m-zh-cndocsv27userexamplesrouting-rule-deprecated-check> |
| <label for=m-zh-cndocsv27userexamplesrouting-rule-deprecated-check><a href=/zh-cn/docsv2.7/user/examples/routing-rule-deprecated/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesrouting-rule-deprecated><span>旧路由规则</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesconfig-rule-li><input type=checkbox id=m-zh-cndocsv27userexamplesconfig-rule-check> |
| <label for=m-zh-cndocsv27userexamplesconfig-rule-check><a href=/zh-cn/docsv2.7/user/examples/config-rule/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesconfig-rule><span>配置规则</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesservice-downgrade-li><input type=checkbox id=m-zh-cndocsv27userexamplesservice-downgrade-check> |
| <label for=m-zh-cndocsv27userexamplesservice-downgrade-check><a href=/zh-cn/docsv2.7/user/examples/service-downgrade/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesservice-downgrade><span>服务降级</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesconfig-rule-deprecated-li><input type=checkbox id=m-zh-cndocsv27userexamplesconfig-rule-deprecated-check> |
| <label for=m-zh-cndocsv27userexamplesconfig-rule-deprecated-check><a href=/zh-cn/docsv2.7/user/examples/config-rule-deprecated/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesconfig-rule-deprecated><span>旧配置规则</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesconsumer-threadpool-li><input type=checkbox id=m-zh-cndocsv27userexamplesconsumer-threadpool-check> |
| <label for=m-zh-cndocsv27userexamplesconsumer-threadpool-check><a href=/zh-cn/docsv2.7/user/examples/consumer-threadpool/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesconsumer-threadpool><span>消费端线程池模型</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesgraceful-shutdown-li><input type=checkbox id=m-zh-cndocsv27userexamplesgraceful-shutdown-check> |
| <label for=m-zh-cndocsv27userexamplesgraceful-shutdown-check><a href=/zh-cn/docsv2.7/user/examples/graceful-shutdown/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesgraceful-shutdown><span>优雅停机</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexampleshostname-binding-li><input type=checkbox id=m-zh-cndocsv27userexampleshostname-binding-check> |
| <label for=m-zh-cndocsv27userexampleshostname-binding-check><a href=/zh-cn/docsv2.7/user/examples/hostname-binding/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexampleshostname-binding><span>主机绑定</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userexamplesset-host-li><input type=checkbox id=m-zh-cndocsv27userexamplesset-host-check> |
| <label for=m-zh-cndocsv27userexamplesset-host-check><a href=/zh-cn/docsv2.7/user/examples/set-host/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userexamplesset-host><span>主机配置</span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27userreferences-li><input type=checkbox id=m-zh-cndocsv27userreferences-check> |
| <label for=m-zh-cndocsv27userreferences-check><a href=/zh-cn/docsv2.7/user/references/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27userreferences><span>参考手册</span></a></label><ul class="ul-3 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27userreferencesxml-li><input type=checkbox id=m-zh-cndocsv27userreferencesxml-check> |
| <label for=m-zh-cndocsv27userreferencesxml-check><a href=/zh-cn/docsv2.7/user/references/xml/ title="Schema 配置参考手册" class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27userreferencesxml><span>XML 配置</span></a></label><ul class="ul-4 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-application-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-application-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-application-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-application/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-application><span>dubbo:application</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-argument-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-argument-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-argument-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-argument/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-argument><span>dubbo:argument</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-config-center-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-config-center-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-config-center-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-config-center/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-config-center><span>dubbo:config-center</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-consumer-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-consumer-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-consumer-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-consumer/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-consumer><span>dubbo:consumer</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-method-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-method-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-method-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-method/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-method><span>dubbo:method</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-module-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-module-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-module-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-module/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-module><span>dubbo:module</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-monitor-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-monitor-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-monitor-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-monitor/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-monitor><span>dubbo:monitor</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-parameter-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-parameter-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-parameter-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-parameter/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-parameter><span>dubbo:parameter</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-protocol-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-protocol-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-protocol-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-protocol/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-protocol><span>dubbo:protocol</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-provider-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-provider-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-provider-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-provider/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-provider><span>dubbo:provider</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-reference-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-reference-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-reference-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-reference/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-reference><span>dubbo:reference</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-registry-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-registry-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-registry-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-registry/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-registry><span>dubbo:registry</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesxmldubbo-service-li><input type=checkbox id=m-zh-cndocsv27userreferencesxmldubbo-service-check> |
| <label for=m-zh-cndocsv27userreferencesxmldubbo-service-check><a href=/zh-cn/docsv2.7/user/references/xml/dubbo-service/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesxmldubbo-service><span>dubbo:service</span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27userreferencesprotocol-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocol-check> |
| <label for=m-zh-cndocsv27userreferencesprotocol-check><a href=/zh-cn/docsv2.7/user/references/protocol/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27userreferencesprotocol><span>协议参考手册</span></a></label><ul class="ul-4 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocoldubbo-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocoldubbo-check> |
| <label for=m-zh-cndocsv27userreferencesprotocoldubbo-check><a href=/zh-cn/docsv2.7/user/references/protocol/dubbo/ title="dubbo 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocoldubbo><span>dubbo://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolrest-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolrest-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolrest-check><a href=/zh-cn/docsv2.7/user/references/protocol/rest/ title="rest 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolrest><span>rest://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolhttp-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolhttp-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolhttp-check><a href=/zh-cn/docsv2.7/user/references/protocol/http/ title="http 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolhttp><span>http://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolhessian-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolhessian-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolhessian-check><a href=/zh-cn/docsv2.7/user/references/protocol/hessian/ title="hessian 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolhessian><span>hessian://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolredis-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolredis-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolredis-check><a href=/zh-cn/docsv2.7/user/references/protocol/redis/ title="redis 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolredis><span>redis://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolthrift-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolthrift-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolthrift-check><a href=/zh-cn/docsv2.7/user/references/protocol/thrift/ title="thrift 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolthrift><span>thrift://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolgrpc-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolgrpc-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolgrpc-check><a href=/zh-cn/docsv2.7/user/references/protocol/grpc/ title="gRPC 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolgrpc><span>grpc://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolmemcached-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolmemcached-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolmemcached-check><a href=/zh-cn/docsv2.7/user/references/protocol/memcached/ title="memcached 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolmemcached><span>memcached://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolrmi-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolrmi-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolrmi-check><a href=/zh-cn/docsv2.7/user/references/protocol/rmi/ title="rmi 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolrmi><span>rmi://</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesprotocolwebservice-li><input type=checkbox id=m-zh-cndocsv27userreferencesprotocolwebservice-check> |
| <label for=m-zh-cndocsv27userreferencesprotocolwebservice-check><a href=/zh-cn/docsv2.7/user/references/protocol/webservice/ title="webservice 协议" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesprotocolwebservice><span>webservice://</span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27userreferencesregistry-li><input type=checkbox id=m-zh-cndocsv27userreferencesregistry-check> |
| <label for=m-zh-cndocsv27userreferencesregistry-check><a href=/zh-cn/docsv2.7/user/references/registry/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27userreferencesregistry><span>注册中心参考手册</span></a></label><ul class="ul-4 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesregistrynacos-li><input type=checkbox id=m-zh-cndocsv27userreferencesregistrynacos-check> |
| <label for=m-zh-cndocsv27userreferencesregistrynacos-check><a href=/zh-cn/docsv2.7/user/references/registry/nacos/ title="Nacos 注册中心" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesregistrynacos><span>Nacos</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesregistryzookeeper-li><input type=checkbox id=m-zh-cndocsv27userreferencesregistryzookeeper-check> |
| <label for=m-zh-cndocsv27userreferencesregistryzookeeper-check><a href=/zh-cn/docsv2.7/user/references/registry/zookeeper/ title="Zookeeper 注册中心" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesregistryzookeeper><span>Zookeeper</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesregistrymulticast-li><input type=checkbox id=m-zh-cndocsv27userreferencesregistrymulticast-check> |
| <label for=m-zh-cndocsv27userreferencesregistrymulticast-check><a href=/zh-cn/docsv2.7/user/references/registry/multicast/ title="Multicast 注册中心" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesregistrymulticast><span>Multicast</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesregistryredis-li><input type=checkbox id=m-zh-cndocsv27userreferencesregistryredis-check> |
| <label for=m-zh-cndocsv27userreferencesregistryredis-check><a href=/zh-cn/docsv2.7/user/references/registry/redis/ title="Redis 注册中心" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesregistryredis><span>Redis</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesregistrysimple-li><input type=checkbox id=m-zh-cndocsv27userreferencesregistrysimple-check> |
| <label for=m-zh-cndocsv27userreferencesregistrysimple-check><a href=/zh-cn/docsv2.7/user/references/registry/simple/ title="Simple 注册中心" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesregistrysimple><span>Simple</span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesmetadata-li><input type=checkbox id=m-zh-cndocsv27userreferencesmetadata-check> |
| <label for=m-zh-cndocsv27userreferencesmetadata-check><a href=/zh-cn/docsv2.7/user/references/metadata/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesmetadata><span>元数据参考手册</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesapi-li><input type=checkbox id=m-zh-cndocsv27userreferencesapi-check> |
| <label for=m-zh-cndocsv27userreferencesapi-check><a href=/zh-cn/docsv2.7/user/references/api/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesapi><span>API 参考手册</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesqos-li><input type=checkbox id=m-zh-cndocsv27userreferencesqos-check> |
| <label for=m-zh-cndocsv27userreferencesqos-check><a href=/zh-cn/docsv2.7/user/references/qos/ title=在线运维命令参考手册 class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesqos><span>QOS 手册</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencestelnet-li><input type=checkbox id=m-zh-cndocsv27userreferencestelnet-check> |
| <label for=m-zh-cndocsv27userreferencestelnet-check><a href=/zh-cn/docsv2.7/user/references/telnet/ title="Telnet 命令参考手册" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencestelnet><span>Telnet 手册</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userreferencesmaven-li><input type=checkbox id=m-zh-cndocsv27userreferencesmaven-check> |
| <label for=m-zh-cndocsv27userreferencesmaven-check><a href=/zh-cn/docsv2.7/user/references/maven/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userreferencesmaven><span>Maven 插件参考手册</span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27userversions-li><input type=checkbox id=m-zh-cndocsv27userversions-check> |
| <label for=m-zh-cndocsv27userversions-check><a href=/zh-cn/docsv2.7/user/versions/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27userversions><span>版本升级</span></a></label><ul class="ul-3 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userversionsversion-270-li><input type=checkbox id=m-zh-cndocsv27userversionsversion-270-check> |
| <label for=m-zh-cndocsv27userversionsversion-270-check><a href=/zh-cn/docsv2.7/user/versions/version-270/ title=升级与可能的兼容性问题总结 class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userversionsversion-270><span>2.7.0</span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userbest-practice-li><input type=checkbox id=m-zh-cndocsv27userbest-practice-check> |
| <label for=m-zh-cndocsv27userbest-practice-check><a href=/zh-cn/docsv2.7/user/best-practice/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userbest-practice><span>服务化最佳实践</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userrecommend-li><input type=checkbox id=m-zh-cndocsv27userrecommend-check> |
| <label for=m-zh-cndocsv27userrecommend-check><a href=/zh-cn/docsv2.7/user/recommend/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userrecommend><span>推荐用法</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27usercapacity-plan-li><input type=checkbox id=m-zh-cndocsv27usercapacity-plan-check> |
| <label for=m-zh-cndocsv27usercapacity-plan-check><a href=/zh-cn/docsv2.7/user/capacity-plan/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27usercapacity-plan><span>容量规划</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userperf-test-li><input type=checkbox id=m-zh-cndocsv27userperf-test-check> |
| <label for=m-zh-cndocsv27userperf-test-check><a href=/zh-cn/docsv2.7/user/perf-test/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userperf-test><span>性能测试报告</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27usercoveragence-li><input type=checkbox id=m-zh-cndocsv27usercoveragence-check> |
| <label for=m-zh-cndocsv27usercoveragence-check><a href=/zh-cn/docsv2.7/user/coveragence/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27usercoveragence><span>测试覆盖率报告</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userbenchmark-tool-li><input type=checkbox id=m-zh-cndocsv27userbenchmark-tool-check> |
| <label for=m-zh-cndocsv27userbenchmark-tool-check><a href=/zh-cn/docsv2.7/user/benchmark-tool/ title=基准测试工具包 class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userbenchmark-tool><span>基准测试</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userrest-li><input type=checkbox id=m-zh-cndocsv27userrest-check> |
| <label for=m-zh-cndocsv27userrest-check><a href=/zh-cn/docsv2.7/user/rest/ title="开发 REST 应用" class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userrest><span>REST 支持</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27usersimple-monitor-li><input type=checkbox id=m-zh-cndocsv27usersimple-monitor-check> |
| <label for=m-zh-cndocsv27usersimple-monitor-check><a href=/zh-cn/docsv2.7/user/simple-monitor/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27usersimple-monitor><span>简单监控</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userserialization-li><input type=checkbox id=m-zh-cndocsv27userserialization-check> |
| <label for=m-zh-cndocsv27userserialization-check><a href=/zh-cn/docsv2.7/user/serialization/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userserialization><span>Kryo 和 FST 序列化</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27userlanguages-li><input type=checkbox id=m-zh-cndocsv27userlanguages-check> |
| <label for=m-zh-cndocsv27userlanguages-check><a href=/zh-cn/docsv2.7/user/languages/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27userlanguages><span>其他语言支持</span></a></label><ul class="ul-3 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27userlanguageserlang-li><input type=checkbox id=m-zh-cndocsv27userlanguageserlang-check> |
| <label for=m-zh-cndocsv27userlanguageserlang-check><a href=/zh-cn/docsv2.7/user/languages/erlang/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27userlanguageserlang><span>Erlang</span></a></label><ul class="ul-4 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userlanguageserlangquick-start-li><input type=checkbox id=m-zh-cndocsv27userlanguageserlangquick-start-check> |
| <label for=m-zh-cndocsv27userlanguageserlangquick-start-check><a href=/zh-cn/docsv2.7/user/languages/erlang/quick-start/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userlanguageserlangquick-start><span>快速开始</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userlanguageserlangreference-li><input type=checkbox id=m-zh-cndocsv27userlanguageserlangreference-check> |
| <label for=m-zh-cndocsv27userlanguageserlangreference-check><a href=/zh-cn/docsv2.7/user/languages/erlang/reference/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userlanguageserlangreference><span>消费者配置</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userlanguageserlangservice-li><input type=checkbox id=m-zh-cndocsv27userlanguageserlangservice-check> |
| <label for=m-zh-cndocsv27userlanguageserlangservice-check><a href=/zh-cn/docsv2.7/user/languages/erlang/service/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userlanguageserlangservice><span>提供者配置</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27userlanguageserlangserialization-li><input type=checkbox id=m-zh-cndocsv27userlanguageserlangserialization-check> |
| <label for=m-zh-cndocsv27userlanguageserlangserialization-check><a href=/zh-cn/docsv2.7/user/languages/erlang/serialization/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27userlanguageserlangserialization><span>序列化配置项</span></a></label></li></ul></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27usernew-features-in-a-glance-li><input type=checkbox id=m-zh-cndocsv27usernew-features-in-a-glance-check> |
| <label for=m-zh-cndocsv27usernew-features-in-a-glance-check><a href=/zh-cn/docsv2.7/user/new-features-in-a-glance/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27usernew-features-in-a-glance><span></span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27dev-li><input type=checkbox id=m-zh-cndocsv27dev-check> |
| <label for=m-zh-cndocsv27dev-check><a href=/zh-cn/docsv2.7/dev/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27dev><span>开发指南</span></a></label><ul class="ul-2 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devbuild-li><input type=checkbox id=m-zh-cndocsv27devbuild-check> |
| <label for=m-zh-cndocsv27devbuild-check><a href=/zh-cn/docsv2.7/dev/build/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devbuild><span>源码构建</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devdesign-li><input type=checkbox id=m-zh-cndocsv27devdesign-check> |
| <label for=m-zh-cndocsv27devdesign-check><a href=/zh-cn/docsv2.7/dev/design/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devdesign><span>框架设计</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devspi-li><input type=checkbox id=m-zh-cndocsv27devspi-check> |
| <label for=m-zh-cndocsv27devspi-check><a href=/zh-cn/docsv2.7/dev/spi/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devspi><span>扩展点加载</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplementation-li><input type=checkbox id=m-zh-cndocsv27devimplementation-check> |
| <label for=m-zh-cndocsv27devimplementation-check><a href=/zh-cn/docsv2.7/dev/implementation/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplementation><span>实现细节</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27devimpls-li><input type=checkbox id=m-zh-cndocsv27devimpls-check> |
| <label for=m-zh-cndocsv27devimpls-check><a href=/zh-cn/docsv2.7/dev/impls/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27devimpls><span>SPI 扩展实现</span></a></label><ul class="ul-3 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsprotocol-li><input type=checkbox id=m-zh-cndocsv27devimplsprotocol-check> |
| <label for=m-zh-cndocsv27devimplsprotocol-check><a href=/zh-cn/docsv2.7/dev/impls/protocol/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsprotocol><span>协议扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsfilter-li><input type=checkbox id=m-zh-cndocsv27devimplsfilter-check> |
| <label for=m-zh-cndocsv27devimplsfilter-check><a href=/zh-cn/docsv2.7/dev/impls/filter/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsfilter><span>调用拦截扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsinvoker-listener-li><input type=checkbox id=m-zh-cndocsv27devimplsinvoker-listener-check> |
| <label for=m-zh-cndocsv27devimplsinvoker-listener-check><a href=/zh-cn/docsv2.7/dev/impls/invoker-listener/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsinvoker-listener><span>引用监听扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsexporter-listener-li><input type=checkbox id=m-zh-cndocsv27devimplsexporter-listener-check> |
| <label for=m-zh-cndocsv27devimplsexporter-listener-check><a href=/zh-cn/docsv2.7/dev/impls/exporter-listener/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsexporter-listener><span>暴露监听扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplscluster-li><input type=checkbox id=m-zh-cndocsv27devimplscluster-check> |
| <label for=m-zh-cndocsv27devimplscluster-check><a href=/zh-cn/docsv2.7/dev/impls/cluster/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplscluster><span>集群扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsrouter-li><input type=checkbox id=m-zh-cndocsv27devimplsrouter-check> |
| <label for=m-zh-cndocsv27devimplsrouter-check><a href=/zh-cn/docsv2.7/dev/impls/router/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsrouter><span>路由扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsload-balance-li><input type=checkbox id=m-zh-cndocsv27devimplsload-balance-check> |
| <label for=m-zh-cndocsv27devimplsload-balance-check><a href=/zh-cn/docsv2.7/dev/impls/load-balance/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsload-balance><span>负载均衡扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsmerger-li><input type=checkbox id=m-zh-cndocsv27devimplsmerger-check> |
| <label for=m-zh-cndocsv27devimplsmerger-check><a href=/zh-cn/docsv2.7/dev/impls/merger/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsmerger><span>合并结果扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsregistry-li><input type=checkbox id=m-zh-cndocsv27devimplsregistry-check> |
| <label for=m-zh-cndocsv27devimplsregistry-check><a href=/zh-cn/docsv2.7/dev/impls/registry/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsregistry><span>注册中心扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsmonitor-li><input type=checkbox id=m-zh-cndocsv27devimplsmonitor-check> |
| <label for=m-zh-cndocsv27devimplsmonitor-check><a href=/zh-cn/docsv2.7/dev/impls/monitor/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsmonitor><span>监控中心扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsextension-factory-li><input type=checkbox id=m-zh-cndocsv27devimplsextension-factory-check> |
| <label for=m-zh-cndocsv27devimplsextension-factory-check><a href=/zh-cn/docsv2.7/dev/impls/extension-factory/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsextension-factory><span>扩展点加载扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsproxy-factory-li><input type=checkbox id=m-zh-cndocsv27devimplsproxy-factory-check> |
| <label for=m-zh-cndocsv27devimplsproxy-factory-check><a href=/zh-cn/docsv2.7/dev/impls/proxy-factory/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsproxy-factory><span>动态代理扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplscompiler-li><input type=checkbox id=m-zh-cndocsv27devimplscompiler-check> |
| <label for=m-zh-cndocsv27devimplscompiler-check><a href=/zh-cn/docsv2.7/dev/impls/compiler/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplscompiler><span>编译器扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsconfig-center-li><input type=checkbox id=m-zh-cndocsv27devimplsconfig-center-check> |
| <label for=m-zh-cndocsv27devimplsconfig-center-check><a href=/zh-cn/docsv2.7/dev/impls/config-center/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsconfig-center><span>配置中心扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsdispatcher-li><input type=checkbox id=m-zh-cndocsv27devimplsdispatcher-check> |
| <label for=m-zh-cndocsv27devimplsdispatcher-check><a href=/zh-cn/docsv2.7/dev/impls/dispatcher/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsdispatcher><span>消息派发扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsthreadpool-li><input type=checkbox id=m-zh-cndocsv27devimplsthreadpool-check> |
| <label for=m-zh-cndocsv27devimplsthreadpool-check><a href=/zh-cn/docsv2.7/dev/impls/threadpool/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsthreadpool><span>线程池扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsserialize-li><input type=checkbox id=m-zh-cndocsv27devimplsserialize-check> |
| <label for=m-zh-cndocsv27devimplsserialize-check><a href=/zh-cn/docsv2.7/dev/impls/serialize/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsserialize><span>序列化扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsremoting-li><input type=checkbox id=m-zh-cndocsv27devimplsremoting-check> |
| <label for=m-zh-cndocsv27devimplsremoting-check><a href=/zh-cn/docsv2.7/dev/impls/remoting/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsremoting><span>网络传输扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsexchanger-li><input type=checkbox id=m-zh-cndocsv27devimplsexchanger-check> |
| <label for=m-zh-cndocsv27devimplsexchanger-check><a href=/zh-cn/docsv2.7/dev/impls/exchanger/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsexchanger><span>信息交换扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsnetworker-li><input type=checkbox id=m-zh-cndocsv27devimplsnetworker-check> |
| <label for=m-zh-cndocsv27devimplsnetworker-check><a href=/zh-cn/docsv2.7/dev/impls/networker/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsnetworker><span>组网扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplstelnet-handler-li><input type=checkbox id=m-zh-cndocsv27devimplstelnet-handler-check> |
| <label for=m-zh-cndocsv27devimplstelnet-handler-check><a href=/zh-cn/docsv2.7/dev/impls/telnet-handler/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplstelnet-handler><span>Telnet 命令扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsstatus-checker-li><input type=checkbox id=m-zh-cndocsv27devimplsstatus-checker-check> |
| <label for=m-zh-cndocsv27devimplsstatus-checker-check><a href=/zh-cn/docsv2.7/dev/impls/status-checker/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsstatus-checker><span>状态检查扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplscontainer-li><input type=checkbox id=m-zh-cndocsv27devimplscontainer-check> |
| <label for=m-zh-cndocsv27devimplscontainer-check><a href=/zh-cn/docsv2.7/dev/impls/container/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplscontainer><span>容器扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplscache-li><input type=checkbox id=m-zh-cndocsv27devimplscache-check> |
| <label for=m-zh-cndocsv27devimplscache-check><a href=/zh-cn/docsv2.7/dev/impls/cache/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplscache><span>缓存扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplsvalidation-li><input type=checkbox id=m-zh-cndocsv27devimplsvalidation-check> |
| <label for=m-zh-cndocsv27devimplsvalidation-check><a href=/zh-cn/docsv2.7/dev/impls/validation/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplsvalidation><span>验证扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplslogger-adapter-li><input type=checkbox id=m-zh-cndocsv27devimplslogger-adapter-check> |
| <label for=m-zh-cndocsv27devimplslogger-adapter-check><a href=/zh-cn/docsv2.7/dev/impls/logger-adapter/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplslogger-adapter><span>日志适配扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devimplspage-li><input type=checkbox id=m-zh-cndocsv27devimplspage-check> |
| <label for=m-zh-cndocsv27devimplspage-check><a href=/zh-cn/docsv2.7/dev/impls/page/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devimplspage><span></span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27devprincipals-li><input type=checkbox id=m-zh-cndocsv27devprincipals-check> |
| <label for=m-zh-cndocsv27devprincipals-check><a href=/zh-cn/docsv2.7/dev/principals/ class="align-left pl-0 td-sidebar-link td-sidebar-link__section" id=m-zh-cndocsv27devprincipals><span>设计原则</span></a></label><ul class="ul-3 foldable"><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devprincipalscode-detail-li><input type=checkbox id=m-zh-cndocsv27devprincipalscode-detail-check> |
| <label for=m-zh-cndocsv27devprincipalscode-detail-check><a href=/zh-cn/docsv2.7/dev/principals/code-detail/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devprincipalscode-detail><span>魔鬼在细节</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devprincipalsconfiguration-li><input type=checkbox id=m-zh-cndocsv27devprincipalsconfiguration-check> |
| <label for=m-zh-cndocsv27devprincipalsconfiguration-check><a href=/zh-cn/docsv2.7/dev/principals/configuration/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devprincipalsconfiguration><span>配置设计</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devprincipalsdummy-li><input type=checkbox id=m-zh-cndocsv27devprincipalsdummy-check> |
| <label for=m-zh-cndocsv27devprincipalsdummy-check><a href=/zh-cn/docsv2.7/dev/principals/dummy/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devprincipalsdummy><span>防痴呆设计</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devprincipalsexpansibility-li><input type=checkbox id=m-zh-cndocsv27devprincipalsexpansibility-check> |
| <label for=m-zh-cndocsv27devprincipalsexpansibility-check><a href=/zh-cn/docsv2.7/dev/principals/expansibility/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devprincipalsexpansibility><span>谈谈扩充式扩展与增量式扩展</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devprincipalsextension-li><input type=checkbox id=m-zh-cndocsv27devprincipalsextension-check> |
| <label for=m-zh-cndocsv27devprincipalsextension-check><a href=/zh-cn/docsv2.7/dev/principals/extension/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devprincipalsextension><span>扩展点重构</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devprincipalsgeneral-knowledge-li><input type=checkbox id=m-zh-cndocsv27devprincipalsgeneral-knowledge-check> |
| <label for=m-zh-cndocsv27devprincipalsgeneral-knowledge-check><a href=/zh-cn/docsv2.7/dev/principals/general-knowledge/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devprincipalsgeneral-knowledge><span>一些设计上的基本常识</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devprincipalsrobustness-li><input type=checkbox id=m-zh-cndocsv27devprincipalsrobustness-check> |
| <label for=m-zh-cndocsv27devprincipalsrobustness-check><a href=/zh-cn/docsv2.7/dev/principals/robustness/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devprincipalsrobustness><span>设计实现的健壮性</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devprincipalsintroduction-li><input type=checkbox id=m-zh-cndocsv27devprincipalsintroduction-check> |
| <label for=m-zh-cndocsv27devprincipalsintroduction-check><a href=/zh-cn/docsv2.7/dev/principals/introduction/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devprincipalsintroduction><span></span></a></label></li></ul></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section without-child" id=m-zh-cndocsv27devcontract-li><input type=checkbox id=m-zh-cndocsv27devcontract-check> |
| <label for=m-zh-cndocsv27devcontract-check><a href=/zh-cn/docsv2.7/dev/contract/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27devcontract><span>公共契约</span></a></label></li><li class="td-sidebar-nav__section-title td-sidebar-nav__section with-child" id=m-zh-cndocsv27devsource-li><input type=checkbox id=m-zh-cndocsv27devsource-check> |
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| <label for=m-zh-cndocsv27admininstallmonitor-center-check><a href=/zh-cn/docsv2.7/admin/install/monitor-center/ class="align-left pl-0 td-sidebar-link td-sidebar-link__page" id=m-zh-cndocsv27admininstallmonitor-center><span>Simple 监控中心安装</span></a></label></li></ul></li></ul></li></ul></li></ul></nav></div></div><main class="col-12 col-md-9 col-xl-8 pl-md-5" role=main><nav aria-label=breadcrumb class=td-breadcrumbs><ol class=breadcrumb><li class=breadcrumb-item><a href=https://cn.dubbo.apache.org/zh-cn/docsv2.7/>文档 2.x</a></li><li class=breadcrumb-item><a href=https://cn.dubbo.apache.org/zh-cn/docsv2.7/dev/>开发指南</a></li><li class=breadcrumb-item><a href=https://cn.dubbo.apache.org/zh-cn/docsv2.7/dev/source/>源代码</a></li><li class="breadcrumb-item active" aria-current=page><a href=https://cn.dubbo.apache.org/zh-cn/docsv2.7/dev/source/loadbalance/ aria-disabled=true class="btn-link disabled">负载均衡</a></li></ol></nav><div class=td-content><h1>负载均衡</h1><div class=lead>本文介绍了负载均衡的原理和实现细节</div><header class=article-meta></header><h2 id=1简介>1.简介</h2><p>LoadBalance 中文意思为负载均衡，它的职责是将网络请求，或者其他形式的负载“均摊”到不同的机器上。避免集群中部分服务器压力过大，而另一些服务器比较空闲的情况。通过负载均衡，可以让每台服务器获取到适合自己处理能力的负载。在为高负载服务器分流的同时，还可以避免资源浪费，一举两得。负载均衡可分为软件负载均衡和硬件负载均衡。在我们日常开发中，一般很难接触到硬件负载均衡。但软件负载均衡还是可以接触到的，比如 Nginx。在 Dubbo 中，也有负载均衡的概念和相应的实现。Dubbo 需要对服务消费者的调用请求进行分配，避免少数服务提供者负载过大。服务提供者负载过大，会导致部分请求超时。因此将负载均衡到每个服务提供者上，是非常必要的。Dubbo 提供了4种负载均衡实现，分别是基于权重随机算法的 RandomLoadBalance、基于最少活跃调用数算法的 LeastActiveLoadBalance、基于 hash 一致性的 ConsistentHashLoadBalance，以及基于加权轮询算法的 RoundRobinLoadBalance。这几个负载均衡算法代码不是很长，但是想看懂也不是很容易，需要大家对这几个算法的原理有一定了解才行。如果不是很了解，也没不用太担心。我们会在分析每个算法的源码之前，对算法原理进行简单的讲解，帮助大家建立初步的印象。</p><p>本系列文章在编写之初是基于 Dubbo 2.6.4 的，近期，Dubbo 2.6.5 发布了，其中就有针对对负载均衡部分的优化。因此我们在分析完 2.6.4 版本后的源码后，会另外分析 2.6.5 更新的部分。其他的就不多说了，进入正题吧。</p><h2 id=2源码分析>2.源码分析</h2><p>在 Dubbo 中，所有负载均衡实现类均继承自 AbstractLoadBalance，该类实现了 LoadBalance 接口，并封装了一些公共的逻辑。所以在分析负载均衡实现之前，先来看一下 AbstractLoadBalance 的逻辑。首先来看一下负载均衡的入口方法 select，如下：</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>@Override</span> |
| </span></span><span style=display:flex><span><span style=color:#268bd2>public</span> <span style=color:#719e07><</span>T<span style=color:#719e07>></span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>select</span>(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, URL url, Invocation invocation) { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (invokers <span style=color:#719e07>==</span> <span style=color:#cb4b16>null</span> <span style=color:#719e07>||</span> invokers.isEmpty()) |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> <span style=color:#cb4b16>null</span>; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 如果 invokers 列表中仅有一个 Invoker，直接返回即可，无需进行负载均衡</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (invokers.size() <span style=color:#719e07>==</span> 1) |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(0); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 调用 doSelect 方法进行负载均衡，该方法为抽象方法，由子类实现</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> doSelect(invokers, url, invocation); |
| </span></span><span style=display:flex><span>} |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span><span style=color:#268bd2>protected</span> <span style=color:#268bd2>abstract</span> <span style=color:#719e07><</span>T<span style=color:#719e07>></span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>doSelect</span>(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, URL url, Invocation invocation); |
| </span></span></code></pre></div><p>select 方法的逻辑比较简单，首先会检测 invokers 集合的合法性，然后再检测 invokers 集合元素数量。如果只包含一个 Invoker，直接返回该 Inovker 即可。如果包含多个 Invoker，此时需要通过负载均衡算法选择一个 Invoker。具体的负载均衡算法由子类实现，接下来章节会对这些子类一一进行详细分析。</p><p>AbstractLoadBalance 除了实现了 LoadBalance 接口方法，还封装了一些公共逻辑，比如服务提供者权重计算逻辑。具体实现如下：</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>protected</span> <span style=color:#dc322f>int</span> <span style=color:#268bd2>getWeight</span>(Invoker<span style=color:#719e07><?></span> invoker, Invocation invocation) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 从 url 中获取权重 weight 配置值</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> weight <span style=color:#719e07>=</span> invoker.getUrl().getMethodParameter(invocation.getMethodName(), Constants.WEIGHT_KEY, Constants.DEFAULT_WEIGHT); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (weight <span style=color:#719e07>></span> 0) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取服务提供者启动时间戳</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>long</span> timestamp <span style=color:#719e07>=</span> invoker.getUrl().getParameter(Constants.REMOTE_TIMESTAMP_KEY, 0L); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (timestamp <span style=color:#719e07>></span> 0L) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 计算服务提供者运行时长</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> uptime <span style=color:#719e07>=</span> (<span style=color:#dc322f>int</span>) (System.currentTimeMillis() <span style=color:#719e07>-</span> timestamp); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取服务预热时间，默认为10分钟</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> warmup <span style=color:#719e07>=</span> invoker.getUrl().getParameter(Constants.WARMUP_KEY, Constants.DEFAULT_WARMUP); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 如果服务运行时间小于预热时间，则重新计算服务权重，即降权</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (uptime <span style=color:#719e07>></span> 0 <span style=color:#719e07>&&</span> uptime <span style=color:#719e07><</span> warmup) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 重新计算服务权重</span> |
| </span></span><span style=display:flex><span> weight <span style=color:#719e07>=</span> calculateWarmupWeight(uptime, warmup, weight); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> weight; |
| </span></span><span style=display:flex><span>} |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span><span style=color:#268bd2>static</span> <span style=color:#dc322f>int</span> <span style=color:#268bd2>calculateWarmupWeight</span>(<span style=color:#dc322f>int</span> uptime, <span style=color:#dc322f>int</span> warmup, <span style=color:#dc322f>int</span> weight) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 计算权重，下面代码逻辑上形似于 (uptime / warmup) * weight。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 随着服务运行时间 uptime 增大，权重计算值 ww 会慢慢接近配置值 weight</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> ww <span style=color:#719e07>=</span> (<span style=color:#dc322f>int</span>) ((<span style=color:#dc322f>float</span>) uptime <span style=color:#719e07>/</span> ((<span style=color:#dc322f>float</span>) warmup <span style=color:#719e07>/</span> (<span style=color:#dc322f>float</span>) weight)); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> ww <span style=color:#719e07><</span> 1 <span style=color:#719e07>?</span> 1 : (ww <span style=color:#719e07>></span> weight <span style=color:#719e07>?</span> weight : ww); |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>上面是权重的计算过程，该过程主要用于保证当服务运行时长小于服务预热时间时，对服务进行降权，避免让服务在启动之初就处于高负载状态。服务预热是一个优化手段，与此类似的还有 JVM 预热。主要目的是让服务启动后“低功率”运行一段时间，使其效率慢慢提升至最佳状态。</p><p>关于 AbstractLoadBalance 就先分析到这，接下来分析各个实现类的代码。首先，我们从 Dubbo 缺省的实现类 RandomLoadBalance 看起。</p><h3 id=21-randomloadbalance>2.1 RandomLoadBalance</h3><p>RandomLoadBalance 是加权随机算法的具体实现，它的算法思想很简单。假设我们有一组服务器 servers = [A, B, C]，他们对应的权重为 weights = [5, 3, 2]，权重总和为10。现在把这些权重值平铺在一维坐标值上，[0, 5) 区间属于服务器 A，[5, 8) 区间属于服务器 B，[8, 10) 区间属于服务器 C。接下来通过随机数生成器生成一个范围在 [0, 10) 之间的随机数，然后计算这个随机数会落到哪个区间上。比如数字3会落到服务器 A 对应的区间上，此时返回服务器 A 即可。权重越大的机器，在坐标轴上对应的区间范围就越大，因此随机数生成器生成的数字就会有更大的概率落到此区间内。只要随机数生成器产生的随机数分布性很好，在经过多次选择后，每个服务器被选中的次数比例接近其权重比例。比如，经过一万次选择后，服务器 A 被选中的次数大约为5000次，服务器 B 被选中的次数约为3000次，服务器 C 被选中的次数约为2000次。</p><p>以上就是 RandomLoadBalance 背后的算法思想，比较简单。下面开始分析源码。</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>public</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>RandomLoadBalance</span> <span style=color:#268bd2>extends</span> AbstractLoadBalance { |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>final</span> String NAME <span style=color:#719e07>=</span> <span style=color:#2aa198>"random"</span>; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> Random random <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> Random(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>@Override</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>protected</span> <span style=color:#719e07><</span>T<span style=color:#719e07>></span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>doSelect</span>(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, URL url, Invocation invocation) { |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> length <span style=color:#719e07>=</span> invokers.size(); |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> totalWeight <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>boolean</span> sameWeight <span style=color:#719e07>=</span> <span style=color:#cb4b16>true</span>; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 下面这个循环有两个作用，第一是计算总权重 totalWeight，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 第二是检测每个服务提供者的权重是否相同</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> length; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> weight <span style=color:#719e07>=</span> getWeight(invokers.get(i), invocation); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 累加权重</span> |
| </span></span><span style=display:flex><span> totalWeight <span style=color:#719e07>+=</span> weight; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 检测当前服务提供者的权重与上一个服务提供者的权重是否相同，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 不相同的话，则将 sameWeight 置为 false。</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (sameWeight <span style=color:#719e07>&&</span> i <span style=color:#719e07>></span> 0 |
| </span></span><span style=display:flex><span> <span style=color:#719e07>&&</span> weight <span style=color:#719e07>!=</span> getWeight(invokers.get(i <span style=color:#719e07>-</span> 1), invocation)) { |
| </span></span><span style=display:flex><span> sameWeight <span style=color:#719e07>=</span> <span style=color:#cb4b16>false</span>; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 下面的 if 分支主要用于获取随机数，并计算随机数落在哪个区间上</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (totalWeight <span style=color:#719e07>></span> 0 <span style=color:#719e07>&&</span> <span style=color:#719e07>!</span>sameWeight) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 随机获取一个 [0, totalWeight) 区间内的数字</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> offset <span style=color:#719e07>=</span> random.nextInt(totalWeight); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 循环让 offset 数减去服务提供者权重值，当 offset 小于0时，返回相应的 Invoker。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 举例说明一下，我们有 servers = [A, B, C]，weights = [5, 3, 2]，offset = 7。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 第一次循环，offset - 5 = 2 > 0，即 offset > 5，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 表明其不会落在服务器 A 对应的区间上。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 第二次循环，offset - 3 = -1 < 0，即 5 < offset < 8，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 表明其会落在服务器 B 对应的区间上</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> length; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 让随机值 offset 减去权重值</span> |
| </span></span><span style=display:flex><span> offset <span style=color:#719e07>-=</span> getWeight(invokers.get(i), invocation); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (offset <span style=color:#719e07><</span> 0) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 返回相应的 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(i); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 如果所有服务提供者权重值相同，此时直接随机返回一个即可</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(random.nextInt(length)); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>RandomLoadBalance 的算法思想比较简单，在经过多次请求后，能够将调用请求按照权重值进行“均匀”分配。当然 RandomLoadBalance 也存在一定的缺点，当调用次数比较少时，Random 产生的随机数可能会比较集中，此时多数请求会落到同一台服务器上。这个缺点并不是很严重，多数情况下可以忽略。RandomLoadBalance 是一个简单，高效的负载均衡实现，因此 Dubbo 选择它作为缺省实现。</p><p>关于 RandomLoadBalance 就先到这了，接下来分析 LeastActiveLoadBalance。</p><h3 id=22-leastactiveloadbalance>2.2 LeastActiveLoadBalance</h3><p>LeastActiveLoadBalance 翻译过来是最小活跃数负载均衡。活跃调用数越小，表明该服务提供者效率越高，单位时间内可处理更多的请求。此时应优先将请求分配给该服务提供者。在具体实现中，每个服务提供者对应一个活跃数 active。初始情况下，所有服务提供者活跃数均为0。每收到一个请求，活跃数加1，完成请求后则将活跃数减1。在服务运行一段时间后，性能好的服务提供者处理请求的速度更快，因此活跃数下降的也越快，此时这样的服务提供者能够优先获取到新的服务请求、这就是最小活跃数负载均衡算法的基本思想。除了最小活跃数，LeastActiveLoadBalance 在实现上还引入了权重值。所以准确的来说，LeastActiveLoadBalance 是基于加权最小活跃数算法实现的。举个例子说明一下，在一个服务提供者集群中，有两个性能优异的服务提供者。某一时刻它们的活跃数相同，此时 Dubbo 会根据它们的权重去分配请求，权重越大，获取到新请求的概率就越大。如果两个服务提供者权重相同，此时随机选择一个即可。关于 LeastActiveLoadBalance 的背景知识就先介绍到这里，下面开始分析源码。</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>public</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>LeastActiveLoadBalance</span> <span style=color:#268bd2>extends</span> AbstractLoadBalance { |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>final</span> String NAME <span style=color:#719e07>=</span> <span style=color:#2aa198>"leastactive"</span>; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> Random random <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> Random(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>@Override</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>protected</span> <span style=color:#719e07><</span>T<span style=color:#719e07>></span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>doSelect</span>(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, URL url, Invocation invocation) { |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> length <span style=color:#719e07>=</span> invokers.size(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 最小的活跃数</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> leastActive <span style=color:#719e07>=</span> <span style=color:#719e07>-</span>1; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 具有相同“最小活跃数”的服务者提供者（以下用 Invoker 代称）数量</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> leastCount <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// leastIndexs 用于记录具有相同“最小活跃数”的 Invoker 在 invokers 列表中的下标信息</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span><span style=color:#719e07>[]</span> leastIndexs <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> <span style=color:#dc322f>int</span><span style=color:#719e07>[</span>length<span style=color:#719e07>]</span>; |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> totalWeight <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 第一个最小活跃数的 Invoker 权重值，用于与其他具有相同最小活跃数的 Invoker 的权重进行对比，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 以检测是否“所有具有相同最小活跃数的 Invoker 的权重”均相等</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> firstWeight <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>boolean</span> sameWeight <span style=color:#719e07>=</span> <span style=color:#cb4b16>true</span>; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 遍历 invokers 列表</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> length; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> invoker <span style=color:#719e07>=</span> invokers.get(i); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取 Invoker 对应的活跃数</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> active <span style=color:#719e07>=</span> RpcStatus.getStatus(invoker.getUrl(), invocation.getMethodName()).getActive(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取权重 - ⭐️</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> weight <span style=color:#719e07>=</span> invoker.getUrl().getMethodParameter(invocation.getMethodName(), Constants.WEIGHT_KEY, Constants.DEFAULT_WEIGHT); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 发现更小的活跃数，重新开始</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (leastActive <span style=color:#719e07>==</span> <span style=color:#719e07>-</span>1 <span style=color:#719e07>||</span> active <span style=color:#719e07><</span> leastActive) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 使用当前活跃数 active 更新最小活跃数 leastActive</span> |
| </span></span><span style=display:flex><span> leastActive <span style=color:#719e07>=</span> active; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 更新 leastCount 为 1</span> |
| </span></span><span style=display:flex><span> leastCount <span style=color:#719e07>=</span> 1; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 记录当前下标值到 leastIndexs 中</span> |
| </span></span><span style=display:flex><span> leastIndexs<span style=color:#719e07>[</span>0<span style=color:#719e07>]</span> <span style=color:#719e07>=</span> i; |
| </span></span><span style=display:flex><span> totalWeight <span style=color:#719e07>=</span> weight; |
| </span></span><span style=display:flex><span> firstWeight <span style=color:#719e07>=</span> weight; |
| </span></span><span style=display:flex><span> sameWeight <span style=color:#719e07>=</span> <span style=color:#cb4b16>true</span>; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 当前 Invoker 的活跃数 active 与最小活跃数 leastActive 相同 </span> |
| </span></span><span style=display:flex><span> } <span style=color:#719e07>else</span> <span style=color:#719e07>if</span> (active <span style=color:#719e07>==</span> leastActive) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 在 leastIndexs 中记录下当前 Invoker 在 invokers 集合中的下标</span> |
| </span></span><span style=display:flex><span> leastIndexs<span style=color:#719e07>[</span>leastCount<span style=color:#719e07>++]</span> <span style=color:#719e07>=</span> i; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 累加权重</span> |
| </span></span><span style=display:flex><span> totalWeight <span style=color:#719e07>+=</span> weight; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 检测当前 Invoker 的权重与 firstWeight 是否相等，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 不相等则将 sameWeight 置为 false</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (sameWeight <span style=color:#719e07>&&</span> i <span style=color:#719e07>></span> 0 |
| </span></span><span style=display:flex><span> <span style=color:#719e07>&&</span> weight <span style=color:#719e07>!=</span> firstWeight) { |
| </span></span><span style=display:flex><span> sameWeight <span style=color:#719e07>=</span> <span style=color:#cb4b16>false</span>; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 当只有一个 Invoker 具有最小活跃数，此时直接返回该 Invoker 即可</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (leastCount <span style=color:#719e07>==</span> 1) { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(leastIndexs<span style=color:#719e07>[</span>0<span style=color:#719e07>]</span>); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 有多个 Invoker 具有相同的最小活跃数，但它们之间的权重不同</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (<span style=color:#719e07>!</span>sameWeight <span style=color:#719e07>&&</span> totalWeight <span style=color:#719e07>></span> 0) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 随机生成一个 [0, totalWeight) 之间的数字</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> offsetWeight <span style=color:#719e07>=</span> random.nextInt(totalWeight); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 循环让随机数减去具有最小活跃数的 Invoker 的权重值，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 当 offset 小于等于0时，返回相应的 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> leastCount; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> leastIndex <span style=color:#719e07>=</span> leastIndexs<span style=color:#719e07>[</span>i<span style=color:#719e07>]</span>; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取权重值，并让随机数减去权重值 - ⭐️</span> |
| </span></span><span style=display:flex><span> offsetWeight <span style=color:#719e07>-=</span> getWeight(invokers.get(leastIndex), invocation); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (offsetWeight <span style=color:#719e07><=</span> 0) |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(leastIndex); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 如果权重相同或权重为0时，随机返回一个 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(leastIndexs<span style=color:#719e07>[</span>random.nextInt(leastCount)<span style=color:#719e07>]</span>); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>上面代码的逻辑比较多，我们在代码中写了大量的注释，有帮助大家理解代码逻辑。下面简单总结一下以上代码所做的事情，如下：</p><ol><li>遍历 invokers 列表，寻找活跃数最小的 Invoker</li><li>如果有多个 Invoker 具有相同的最小活跃数，此时记录下这些 Invoker 在 invokers 集合中的下标，并累加它们的权重，比较它们的权重值是否相等</li><li>如果只有一个 Invoker 具有最小的活跃数，此时直接返回该 Invoker 即可</li><li>如果有多个 Invoker 具有最小活跃数，且它们的权重不相等，此时处理方式和 RandomLoadBalance 一致</li><li>如果有多个 Invoker 具有最小活跃数，但它们的权重相等，此时随机返回一个即可</li></ol><p>以上就是 LeastActiveLoadBalance 大致的实现逻辑，大家在阅读的源码的过程中要注意区分活跃数与权重这两个概念，不要混为一谈。</p><p>以上分析是基于 Dubbo 2.6.4 版本进行的，由于近期 Dubbo 2.6.5 发布了，并对 LeastActiveLoadBalance 进行了一些修改，下面简单来介绍一下修改内容。回到上面的源码中，我们在上面的代码中标注了两个黄色的五角星⭐️。两处标记对应的代码分别如下：</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#dc322f>int</span> weight <span style=color:#719e07>=</span> invoker.getUrl().getMethodParameter(invocation.getMethodName(), Constants.WEIGHT_KEY, Constants.DEFAULT_WEIGHT); |
| </span></span></code></pre></div><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span>offsetWeight <span style=color:#719e07>-=</span> getWeight(invokers.get(leastIndex), invocation); |
| </span></span></code></pre></div><p>问题出在服务预热阶段，第一行代码直接从 url 中取权重值，未被降权过。第二行代码获取到的是经过降权后的权重。第一行代码获取到的权重值最终会被累加到权重总和 totalWeight 中，这个时候会导致一个问题。offsetWeight 是一个在 [0, totalWeight) 范围内的随机数，而它所减去的是经过降权的权重。很有可能在经过 leastCount 次运算后，offsetWeight 仍然是大于0的，导致无法选中 Invoker。这个问题对应的 issue 为 <a href=https://github.com/apache/dubbo/issues/904>#904</a>，并在 pull request <a href=https://github.com/apache/dubbo/pull/2172>#2172</a> 中被修复。具体的修复逻辑是将标注一处的代码修改为：</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#586e75>// afterWarmup 等价于上面的 weight 变量，这样命名是为了强调该变量经过了 warmup 降权处理</span> |
| </span></span><span style=display:flex><span><span style=color:#dc322f>int</span> afterWarmup <span style=color:#719e07>=</span> getWeight(invoker, invocation); |
| </span></span></code></pre></div><p>另外，2.6.4 版本中的 LeastActiveLoadBalance 还有一个缺陷，即当一组 Invoker 具有相同的最小活跃数，且其中一个 Invoker 的权重值为1，此时这个 Invoker 无法被选中。缺陷代码如下：</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#dc322f>int</span> offsetWeight <span style=color:#719e07>=</span> random.nextInt(totalWeight); |
| </span></span><span style=display:flex><span><span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> leastCount; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> leastIndex <span style=color:#719e07>=</span> leastIndexs<span style=color:#719e07>[</span>i<span style=color:#719e07>]</span>; |
| </span></span><span style=display:flex><span> offsetWeight <span style=color:#719e07>-=</span> getWeight(invokers.get(leastIndex), invocation); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (offsetWeight <span style=color:#719e07><=</span> 0) <span style=color:#586e75>// ❌</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(leastIndex); |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>问题出在了<code>offsetWeight <= 0</code>上，举例说明，假设有一组 Invoker 的权重为 5、2、1，offsetWeight 最大值为 7。假设 offsetWeight = 7，你会发现，当 for 循环进行第二次遍历后 offsetWeight = 7 - 5 - 2 = 0，提前返回了。此时，此时权重为1的 Invoker 就没有机会被选中了。该问题在 Dubbo 2.6.5 中被修复了，修改后的代码如下：</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#dc322f>int</span> offsetWeight <span style=color:#719e07>=</span> random.nextInt(totalWeight) <span style=color:#719e07>+</span> 1; |
| </span></span></code></pre></div><p>以上就是 Dubbo 2.6.5 对 LeastActiveLoadBalance 的更新，内容不是很多，先分析到这。接下来分析基于一致性 hash 思想的 ConsistentHashLoadBalance。</p><h3 id=23-consistenthashloadbalance>2.3 ConsistentHashLoadBalance</h3><p>一致性 hash 算法由麻省理工学院的 Karger 及其合作者于1997年提出的，算法提出之初是用于大规模缓存系统的负载均衡。它的工作过程是这样的，首先根据 ip 或者其他的信息为缓存节点生成一个 hash，并将这个 hash 投射到 [0, 2<sup>32</sup> - 1] 的圆环上。当有查询或写入请求时，则为缓存项的 key 生成一个 hash 值。然后查找第一个大于或等于该 hash 值的缓存节点，并到这个节点中查询或写入缓存项。如果当前节点挂了，则在下一次查询或写入缓存时，为缓存项查找另一个大于其 hash 值的缓存节点即可。大致效果如下图所示，每个缓存节点在圆环上占据一个位置。如果缓存项的 key 的 hash 值小于缓存节点 hash 值，则到该缓存节点中存储或读取缓存项。比如下面绿色点对应的缓存项将会被存储到 cache-2 节点中。由于 cache-3 挂了，原本应该存到该节点中的缓存项最终会存储到 cache-4 节点中。</p><p><img src=/imgs/dev/consistent-hash.jpg alt=img></p><p>下面来看看一致性 hash 在 Dubbo 中的应用。我们把上图的缓存节点替换成 Dubbo 的服务提供者，于是得到了下图：</p><p><img src=/imgs/dev/consistent-hash-invoker.jpg alt=img></p><p>这里相同颜色的节点均属于同一个服务提供者，比如 Invoker1-1，Invoker1-2，……, Invoker1-160。这样做的目的是通过引入虚拟节点，让 Invoker 在圆环上分散开来，避免数据倾斜问题。所谓数据倾斜是指，由于节点不够分散，导致大量请求落到了同一个节点上，而其他节点只会接收到了少量请求的情况。比如：</p><p><img src=/imgs/dev/consistent-hash-data-incline.jpg alt=img></p><p>如上，由于 Invoker-1 和 Invoker-2 在圆环上分布不均，导致系统中75%的请求都会落到 Invoker-1 上，只有 25% 的请求会落到 Invoker-2 上。解决这个问题办法是引入虚拟节点，通过虚拟节点均衡各个节点的请求量。</p><p>到这里背景知识就普及完了，接下来开始分析源码。我们先从 ConsistentHashLoadBalance 的 doSelect 方法开始看起，如下：</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>public</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>ConsistentHashLoadBalance</span> <span style=color:#268bd2>extends</span> AbstractLoadBalance { |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> ConcurrentMap<span style=color:#719e07><</span>String, ConsistentHashSelector<span style=color:#719e07><?>></span> selectors <span style=color:#719e07>=</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>new</span> ConcurrentHashMap<span style=color:#719e07><</span>String, ConsistentHashSelector<span style=color:#719e07><?>></span>(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>@Override</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>protected</span> <span style=color:#719e07><</span>T<span style=color:#719e07>></span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>doSelect</span>(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, URL url, Invocation invocation) { |
| </span></span><span style=display:flex><span> String methodName <span style=color:#719e07>=</span> RpcUtils.getMethodName(invocation); |
| </span></span><span style=display:flex><span> String key <span style=color:#719e07>=</span> invokers.get(0).getUrl().getServiceKey() <span style=color:#719e07>+</span> <span style=color:#2aa198>"."</span> <span style=color:#719e07>+</span> methodName; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取 invokers 原始的 hashcode</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> identityHashCode <span style=color:#719e07>=</span> System.identityHashCode(invokers); |
| </span></span><span style=display:flex><span> ConsistentHashSelector<span style=color:#719e07><</span>T<span style=color:#719e07>></span> selector <span style=color:#719e07>=</span> (ConsistentHashSelector<span style=color:#719e07><</span>T<span style=color:#719e07>></span>) selectors.get(key); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 如果 invokers 是一个新的 List 对象，意味着服务提供者数量发生了变化，可能新增也可能减少了。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 此时 selector.identityHashCode != identityHashCode 条件成立</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (selector <span style=color:#719e07>==</span> <span style=color:#cb4b16>null</span> <span style=color:#719e07>||</span> selector.identityHashCode <span style=color:#719e07>!=</span> identityHashCode) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 创建新的 ConsistentHashSelector</span> |
| </span></span><span style=display:flex><span> selectors.put(key, <span style=color:#719e07>new</span> ConsistentHashSelector<span style=color:#719e07><</span>T<span style=color:#719e07>></span>(invokers, methodName, identityHashCode)); |
| </span></span><span style=display:flex><span> selector <span style=color:#719e07>=</span> (ConsistentHashSelector<span style=color:#719e07><</span>T<span style=color:#719e07>></span>) selectors.get(key); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 调用 ConsistentHashSelector 的 select 方法选择 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> selector.select(invocation); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>final</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>ConsistentHashSelector</span><span style=color:#719e07><</span>T<span style=color:#719e07>></span> {...} |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>如上，doSelect 方法主要做了一些前置工作，比如检测 invokers 列表是不是变动过，以及创建 ConsistentHashSelector。这些工作做完后，接下来开始调用 ConsistentHashSelector 的 select 方法执行负载均衡逻辑。在分析 select 方法之前，我们先来看一下一致性 hash 选择器 ConsistentHashSelector 的初始化过程，如下：</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>private</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>final</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>ConsistentHashSelector</span><span style=color:#719e07><</span>T<span style=color:#719e07>></span> { |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 使用 TreeMap 存储 Invoker 虚拟节点</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> TreeMap<span style=color:#719e07><</span>Long, Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> virtualInvokers; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> <span style=color:#dc322f>int</span> replicaNumber; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> <span style=color:#dc322f>int</span> identityHashCode; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> <span style=color:#dc322f>int</span><span style=color:#719e07>[]</span> argumentIndex; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> ConsistentHashSelector(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, String methodName, <span style=color:#dc322f>int</span> identityHashCode) { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>this</span>.virtualInvokers <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> TreeMap<span style=color:#719e07><</span>Long, Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span>(); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>this</span>.identityHashCode <span style=color:#719e07>=</span> identityHashCode; |
| </span></span><span style=display:flex><span> URL url <span style=color:#719e07>=</span> invokers.get(0).getUrl(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取虚拟节点数，默认为160</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>this</span>.replicaNumber <span style=color:#719e07>=</span> url.getMethodParameter(methodName, <span style=color:#2aa198>"hash.nodes"</span>, 160); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取参与 hash 计算的参数下标值，默认对第一个参数进行 hash 运算</span> |
| </span></span><span style=display:flex><span> String<span style=color:#719e07>[]</span> index <span style=color:#719e07>=</span> Constants.COMMA_SPLIT_PATTERN.split(url.getMethodParameter(methodName, <span style=color:#2aa198>"hash.arguments"</span>, <span style=color:#2aa198>"0"</span>)); |
| </span></span><span style=display:flex><span> argumentIndex <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> <span style=color:#dc322f>int</span><span style=color:#719e07>[</span>index.length<span style=color:#719e07>]</span>; |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> index.length; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> argumentIndex<span style=color:#719e07>[</span>i<span style=color:#719e07>]</span> <span style=color:#719e07>=</span> Integer.parseInt(index<span style=color:#719e07>[</span>i<span style=color:#719e07>]</span>); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> invoker : invokers) { |
| </span></span><span style=display:flex><span> String address <span style=color:#719e07>=</span> invoker.getUrl().getAddress(); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> replicaNumber <span style=color:#719e07>/</span> 4; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 对 address + i 进行 md5 运算，得到一个长度为16的字节数组</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>byte</span><span style=color:#719e07>[]</span> digest <span style=color:#719e07>=</span> md5(address <span style=color:#719e07>+</span> i); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 对 digest 部分字节进行4次 hash 运算，得到四个不同的 long 型正整数</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> h <span style=color:#719e07>=</span> 0; h <span style=color:#719e07><</span> 4; h<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// h = 0 时，取 digest 中下标为 0 ~ 3 的4个字节进行位运算</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// h = 1 时，取 digest 中下标为 4 ~ 7 的4个字节进行位运算</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// h = 2, h = 3 时过程同上</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>long</span> m <span style=color:#719e07>=</span> hash(digest, h); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 将 hash 到 invoker 的映射关系存储到 virtualInvokers 中，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// virtualInvokers 需要提供高效的查询操作，因此选用 TreeMap 作为存储结构</span> |
| </span></span><span style=display:flex><span> virtualInvokers.put(m, invoker); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>ConsistentHashSelector 的构造方法执行了一系列的初始化逻辑，比如从配置中获取虚拟节点数以及参与 hash 计算的参数下标，默认情况下只使用第一个参数进行 hash。需要特别说明的是，ConsistentHashLoadBalance 的负载均衡逻辑只受参数值影响，具有相同参数值的请求将会被分配给同一个服务提供者。ConsistentHashLoadBalance 不 关系权重，因此使用时需要注意一下。</p><p>在获取虚拟节点数和参数下标配置后，接下来要做的事情是计算虚拟节点 hash 值，并将虚拟节点存储到 TreeMap 中。到此，ConsistentHashSelector 初始化工作就完成了。接下来，我们来看看 select 方法的逻辑。</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>public</span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>select</span>(Invocation invocation) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 将参数转为 key</span> |
| </span></span><span style=display:flex><span> String key <span style=color:#719e07>=</span> toKey(invocation.getArguments()); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 对参数 key 进行 md5 运算</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>byte</span><span style=color:#719e07>[]</span> digest <span style=color:#719e07>=</span> md5(key); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 取 digest 数组的前四个字节进行 hash 运算，再将 hash 值传给 selectForKey 方法，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 寻找合适的 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> selectForKey(hash(digest, 0)); |
| </span></span><span style=display:flex><span>} |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span><span style=color:#268bd2>private</span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>selectForKey</span>(<span style=color:#dc322f>long</span> hash) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 到 TreeMap 中查找第一个节点值大于或等于当前 hash 的 Invoker</span> |
| </span></span><span style=display:flex><span> Map.Entry<span style=color:#719e07><</span>Long, Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> entry <span style=color:#719e07>=</span> virtualInvokers.tailMap(hash, <span style=color:#cb4b16>true</span>).firstEntry(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 如果 hash 大于 Invoker 在圆环上最大的位置，此时 entry = null，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 需要将 TreeMap 的头节点赋值给 entry</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (entry <span style=color:#719e07>==</span> <span style=color:#cb4b16>null</span>) { |
| </span></span><span style=display:flex><span> entry <span style=color:#719e07>=</span> virtualInvokers.firstEntry(); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 返回 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> entry.getValue(); |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>如上，选择的过程相对比较简单了。首先是对参数进行 md5 以及 hash 运算，得到一个 hash 值。然后再拿这个值到 TreeMap 中查找目标 Invoker 即可。</p><p>到此关于 ConsistentHashLoadBalance 就分析完了。在阅读 ConsistentHashLoadBalance 源码之前，大家一定要先补充背景知识，不然很难看懂代码逻辑。</p><h3 id=24-roundrobinloadbalance>2.4 RoundRobinLoadBalance</h3><p>本节，我们来看一下 Dubbo 中加权轮询负载均衡的实现 RoundRobinLoadBalance。在详细分析源码前，我们先来了解一下什么是加权轮询。这里从最简单的轮询开始讲起，所谓轮询是指将请求轮流分配给每台服务器。举个例子，我们有三台服务器 A、B、C。我们将第一个请求分配给服务器 A，第二个请求分配给服务器 B，第三个请求分配给服务器 C，第四个请求再次分配给服务器 A。这个过程就叫做轮询。轮询是一种无状态负载均衡算法，实现简单，适用于每台服务器性能相近的场景下。但现实情况下，我们并不能保证每台服务器性能均相近。如果我们将等量的请求分配给性能较差的服务器，这显然是不合理的。因此，这个时候我们需要对轮询过程进行加权，以调控每台服务器的负载。经过加权后，每台服务器能够得到的请求数比例，接近或等于他们的权重比。比如服务器 A、B、C 权重比为 5:2:1。那么在8次请求中，服务器 A 将收到其中的5次请求，服务器 B 会收到其中的2次请求，服务器 C 则收到其中的1次请求。</p><p>以上就是加权轮询的算法思想，搞懂了这个思想，接下来我们就可以分析源码了。我们先来看一下 2.6.4 版本的 RoundRobinLoadBalance。</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>public</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>RoundRobinLoadBalance</span> <span style=color:#268bd2>extends</span> AbstractLoadBalance { |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>final</span> String NAME <span style=color:#719e07>=</span> <span style=color:#2aa198>"roundrobin"</span>; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> ConcurrentMap<span style=color:#719e07><</span>String, AtomicPositiveInteger<span style=color:#719e07>></span> sequences <span style=color:#719e07>=</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>new</span> ConcurrentHashMap<span style=color:#719e07><</span>String, AtomicPositiveInteger<span style=color:#719e07>></span>(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>@Override</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>protected</span> <span style=color:#719e07><</span>T<span style=color:#719e07>></span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>doSelect</span>(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, URL url, Invocation invocation) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// key = 全限定类名 + "." + 方法名，比如 com.xxx.DemoService.sayHello</span> |
| </span></span><span style=display:flex><span> String key <span style=color:#719e07>=</span> invokers.get(0).getUrl().getServiceKey() <span style=color:#719e07>+</span> <span style=color:#2aa198>"."</span> <span style=color:#719e07>+</span> invocation.getMethodName(); |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> length <span style=color:#719e07>=</span> invokers.size(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 最大权重</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> maxWeight <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 最小权重</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> minWeight <span style=color:#719e07>=</span> Integer.MAX_VALUE; |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>final</span> LinkedHashMap<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span>, IntegerWrapper<span style=color:#719e07>></span> invokerToWeightMap <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> LinkedHashMap<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span>, IntegerWrapper<span style=color:#719e07>></span>(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 权重总和</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> weightSum <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 下面这个循环主要用于查找最大和最小权重，计算权重总和等</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> length; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> weight <span style=color:#719e07>=</span> getWeight(invokers.get(i), invocation); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取最大和最小权重</span> |
| </span></span><span style=display:flex><span> maxWeight <span style=color:#719e07>=</span> Math.max(maxWeight, weight); |
| </span></span><span style=display:flex><span> minWeight <span style=color:#719e07>=</span> Math.min(minWeight, weight); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (weight <span style=color:#719e07>></span> 0) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 将 weight 封装到 IntegerWrapper 中</span> |
| </span></span><span style=display:flex><span> invokerToWeightMap.put(invokers.get(i), <span style=color:#719e07>new</span> IntegerWrapper(weight)); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 累加权重</span> |
| </span></span><span style=display:flex><span> weightSum <span style=color:#719e07>+=</span> weight; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 查找 key 对应的对应 AtomicPositiveInteger 实例，为空则创建。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 这里可以把 AtomicPositiveInteger 看成一个黑盒，大家只要知道</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// AtomicPositiveInteger 用于记录服务的调用编号即可。至于细节，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 大家如果感兴趣，可以自行分析</span> |
| </span></span><span style=display:flex><span> AtomicPositiveInteger sequence <span style=color:#719e07>=</span> sequences.get(key); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (sequence <span style=color:#719e07>==</span> <span style=color:#cb4b16>null</span>) { |
| </span></span><span style=display:flex><span> sequences.putIfAbsent(key, <span style=color:#719e07>new</span> AtomicPositiveInteger()); |
| </span></span><span style=display:flex><span> sequence <span style=color:#719e07>=</span> sequences.get(key); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取当前的调用编号</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> currentSequence <span style=color:#719e07>=</span> sequence.getAndIncrement(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 如果最小权重小于最大权重，表明服务提供者之间的权重是不相等的</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (maxWeight <span style=color:#719e07>></span> 0 <span style=color:#719e07>&&</span> minWeight <span style=color:#719e07><</span> maxWeight) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 使用调用编号对权重总和进行取余操作</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> mod <span style=color:#719e07>=</span> currentSequence <span style=color:#719e07>%</span> weightSum; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 进行 maxWeight 次遍历</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> maxWeight; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 遍历 invokerToWeightMap</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (Map.Entry<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span>, IntegerWrapper<span style=color:#719e07>></span> each : invokerToWeightMap.entrySet()) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>final</span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> k <span style=color:#719e07>=</span> each.getKey(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取权重包装类 IntegerWrapper</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>final</span> IntegerWrapper v <span style=color:#719e07>=</span> each.getValue(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 如果 mod = 0，且权重大于0，此时返回相应的 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (mod <span style=color:#719e07>==</span> 0 <span style=color:#719e07>&&</span> v.getValue() <span style=color:#719e07>></span> 0) { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> k; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// mod != 0，且权重大于0，此时对权重和 mod 分别进行自减操作</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (v.getValue() <span style=color:#719e07>></span> 0) { |
| </span></span><span style=display:flex><span> v.decrement(); |
| </span></span><span style=display:flex><span> mod<span style=color:#719e07>--</span>; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 服务提供者之间的权重相等，此时通过轮询选择 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(currentSequence <span style=color:#719e07>%</span> length); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// IntegerWrapper 是一个 int 包装类，主要包含了一个自减方法。</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>final</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>IntegerWrapper</span> { |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#dc322f>int</span> value; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#dc322f>void</span> <span style=color:#268bd2>decrement</span>() { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>this</span>.value<span style=color:#719e07>--</span>; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 省略部分代码</span> |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>如上，RoundRobinLoadBalance 的每行代码都不是很难理解，但是将它们组合在一起之后，就不是很好理解了。所以下面我们举例进行说明，假设我们有三台服务器 servers = [A, B, C]，对应的权重为 weights = [2, 5, 1]。接下来对上面的逻辑进行简单的模拟。</p><p>mod = 0：满足条件，此时直接返回服务器 A</p><p>mod = 1：需要进行一次递减操作才能满足条件，此时返回服务器 B</p><p>mod = 2：需要进行两次递减操作才能满足条件，此时返回服务器 C</p><p>mod = 3：需要进行三次递减操作才能满足条件，经过递减后，服务器权重为 [1, 4, 0]，此时返回服务器 A</p><p>mod = 4：需要进行四次递减操作才能满足条件，经过递减后，服务器权重为 [0, 4, 0]，此时返回服务器 B</p><p>mod = 5：需要进行五次递减操作才能满足条件，经过递减后，服务器权重为 [0, 3, 0]，此时返回服务器 B</p><p>mod = 6：需要进行六次递减操作才能满足条件，经过递减后，服务器权重为 [0, 2, 0]，此时返回服务器 B</p><p>mod = 7：需要进行七次递减操作才能满足条件，经过递减后，服务器权重为 [0, 1, 0]，此时返回服务器 B</p><p>经过8次调用后，我们得到的负载均衡结果为 [A, B, C, A, B, B, B, B]，次数比 A:B:C = 2:5:1，等于权重比。当 sequence = 8 时，mod = 0，此时重头再来。从上面的模拟过程可以看出，当 mod >= 3 后，服务器 C 就不会被选中了，因为它的权重被减为0了。当 mod >= 4 后，服务器 A 的权重被减为0，此后 A 就不会再被选中。</p><p>以上是 2.6.4 版本的 RoundRobinLoadBalance 分析过程，2.6.4 版本的 RoundRobinLoadBalance 在某些情况下存在着比较严重的性能问题，该问题最初是在 <a href=https://github.com/apache/dubbo/issues/2578>issue #2578</a> 中被反馈出来。问题出在了 Invoker 的返回时机上，RoundRobinLoadBalance 需要在<code>mod == 0 && v.getValue() > 0</code> 条件成立的情况下才会被返回相应的 Invoker。假如 mod 很大，比如 10000，50000，甚至更大时，doSelect 方法需要进行很多次计算才能将 mod 减为0。由此可知，doSelect 的效率与 mod 有关，时间复杂度为 O(mod)。mod 又受最大权重 maxWeight 的影响，因此当某个服务提供者配置了非常大的权重，此时 RoundRobinLoadBalance 会产生比较严重的性能问题。这个问题被反馈后，社区很快做了回应。并对 RoundRobinLoadBalance 的代码进行了重构，将时间复杂度优化至了常量级别。这个优化可以说很好了，下面我们来学习一下优化后的代码。</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>public</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>RoundRobinLoadBalance</span> <span style=color:#268bd2>extends</span> AbstractLoadBalance { |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>final</span> String NAME <span style=color:#719e07>=</span> <span style=color:#2aa198>"roundrobin"</span>; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> ConcurrentMap<span style=color:#719e07><</span>String, AtomicPositiveInteger<span style=color:#719e07>></span> sequences <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> ConcurrentHashMap<span style=color:#719e07><</span>String, AtomicPositiveInteger<span style=color:#719e07>></span>(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>final</span> ConcurrentMap<span style=color:#719e07><</span>String, AtomicPositiveInteger<span style=color:#719e07>></span> indexSeqs <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> ConcurrentHashMap<span style=color:#719e07><</span>String, AtomicPositiveInteger<span style=color:#719e07>></span>(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>@Override</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>protected</span> <span style=color:#719e07><</span>T<span style=color:#719e07>></span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>doSelect</span>(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, URL url, Invocation invocation) { |
| </span></span><span style=display:flex><span> String key <span style=color:#719e07>=</span> invokers.get(0).getUrl().getServiceKey() <span style=color:#719e07>+</span> <span style=color:#2aa198>"."</span> <span style=color:#719e07>+</span> invocation.getMethodName(); |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> length <span style=color:#719e07>=</span> invokers.size(); |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> maxWeight <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> minWeight <span style=color:#719e07>=</span> Integer.MAX_VALUE; |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>final</span> List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokerToWeightList <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> ArrayList<span style=color:#719e07><></span>(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 查找最大和最小权重</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (<span style=color:#dc322f>int</span> i <span style=color:#719e07>=</span> 0; i <span style=color:#719e07><</span> length; i<span style=color:#719e07>++</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> weight <span style=color:#719e07>=</span> getWeight(invokers.get(i), invocation); |
| </span></span><span style=display:flex><span> maxWeight <span style=color:#719e07>=</span> Math.max(maxWeight, weight); |
| </span></span><span style=display:flex><span> minWeight <span style=color:#719e07>=</span> Math.min(minWeight, weight); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (weight <span style=color:#719e07>></span> 0) { |
| </span></span><span style=display:flex><span> invokerToWeightList.add(invokers.get(i)); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取当前服务对应的调用序列对象 AtomicPositiveInteger</span> |
| </span></span><span style=display:flex><span> AtomicPositiveInteger sequence <span style=color:#719e07>=</span> sequences.get(key); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (sequence <span style=color:#719e07>==</span> <span style=color:#cb4b16>null</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 创建 AtomicPositiveInteger，默认值为0</span> |
| </span></span><span style=display:flex><span> sequences.putIfAbsent(key, <span style=color:#719e07>new</span> AtomicPositiveInteger()); |
| </span></span><span style=display:flex><span> sequence <span style=color:#719e07>=</span> sequences.get(key); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取下标序列对象 AtomicPositiveInteger</span> |
| </span></span><span style=display:flex><span> AtomicPositiveInteger indexSeq <span style=color:#719e07>=</span> indexSeqs.get(key); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (indexSeq <span style=color:#719e07>==</span> <span style=color:#cb4b16>null</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 创建 AtomicPositiveInteger，默认值为 -1</span> |
| </span></span><span style=display:flex><span> indexSeqs.putIfAbsent(key, <span style=color:#719e07>new</span> AtomicPositiveInteger(<span style=color:#719e07>-</span>1)); |
| </span></span><span style=display:flex><span> indexSeq <span style=color:#719e07>=</span> indexSeqs.get(key); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (maxWeight <span style=color:#719e07>></span> 0 <span style=color:#719e07>&&</span> minWeight <span style=color:#719e07><</span> maxWeight) { |
| </span></span><span style=display:flex><span> length <span style=color:#719e07>=</span> invokerToWeightList.size(); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>while</span> (<span style=color:#cb4b16>true</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> index <span style=color:#719e07>=</span> indexSeq.incrementAndGet() <span style=color:#719e07>%</span> length; |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> currentWeight <span style=color:#719e07>=</span> sequence.get() <span style=color:#719e07>%</span> maxWeight; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 每循环一轮（index = 0），重新计算 currentWeight</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (index <span style=color:#719e07>==</span> 0) { |
| </span></span><span style=display:flex><span> currentWeight <span style=color:#719e07>=</span> sequence.incrementAndGet() <span style=color:#719e07>%</span> maxWeight; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 检测 Invoker 的权重是否大于 currentWeight，大于则返回</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (getWeight(invokerToWeightList.get(index), invocation) <span style=color:#719e07>></span> currentWeight) { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokerToWeightList.get(index); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 所有 Invoker 权重相等，此时进行普通的轮询即可</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(sequence.incrementAndGet() <span style=color:#719e07>%</span> length); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>上面代码的逻辑是这样的，每进行一轮循环，重新计算 currentWeight。如果当前 Invoker 权重大于 currentWeight，则返回该 Invoker。下面举例说明，假设服务器 [A, B, C] 对应权重 [5, 2, 1]。</p><p>第一轮循环，currentWeight = 1，可返回 A 和 B</p><p>第二轮循环，currentWeight = 2，返回 A</p><p>第三轮循环，currentWeight = 3，返回 A</p><p>第四轮循环，currentWeight = 4，返回 A</p><p>第五轮循环，currentWeight = 0，返回 A, B, C</p><p>如上，这里的一轮循环是指 index 再次变为0所经历过的循环，这里可以把 index = 0 看做是一轮循环的开始。每一轮循环的次数与 Invoker 的数量有关，Invoker 数量通常不会太多，所以我们可以认为上面代码的时间复杂度为常数级。</p><p>重构后的 RoundRobinLoadBalance 看起来已经很不错了，但是在代码更新不久后，很快又被重构了。这次重构原因是新的 RoundRobinLoadBalance 在某些情况下选出的服务器序列不够均匀。比如，服务器 [A, B, C] 对应权重 [5, 1, 1]。进行7次负载均衡后，选择出来的序列为 [A, A, A, A, A, B, C]。前5个请求全部都落在了服务器 A上，这将会使服务器 A 短时间内接收大量的请求，压力陡增。而 B 和 C 此时无请求，处于空闲状态。而我们期望的结果是这样的 [A, A, B, A, C, A, A]，不同服务器可以穿插获取请求。为了增加负载均衡结果的平滑性，社区再次对 RoundRobinLoadBalance 的实现进行了重构，这次重构参考自 Nginx 的平滑加权轮询负载均衡。每个服务器对应两个权重，分别为 weight 和 currentWeight。其中 weight 是固定的，currentWeight 会动态调整，初始值为0。当有新的请求进来时，遍历服务器列表，让它的 currentWeight 加上自身权重。遍历完成后，找到最大的 currentWeight，并将其减去权重总和，然后返回相应的服务器即可。</p><p>上面描述不是很好理解，下面还是举例进行说明。这里仍然使用服务器 [A, B, C] 对应权重 [5, 1, 1] 的例子说明，现在有7个请求依次进入负载均衡逻辑，选择过程如下：</p><table><thead><tr><th>请求编号</th><th>currentWeight 数组</th><th>选择结果</th><th>减去权重总和后的 currentWeight 数组</th></tr></thead><tbody><tr><td>1</td><td>[5, 1, 1]</td><td>A</td><td>[-2, 1, 1]</td></tr><tr><td>2</td><td>[3, 2, 2]</td><td>A</td><td>[-4, 2, 2]</td></tr><tr><td>3</td><td>[1, 3, 3]</td><td>B</td><td>[1, -4, 3]</td></tr><tr><td>4</td><td>[6, -3, 4]</td><td>A</td><td>[-1, -3, 4]</td></tr><tr><td>5</td><td>[4, -2, 5]</td><td>C</td><td>[4, -2, -2]</td></tr><tr><td>6</td><td>[9, -1, -1]</td><td>A</td><td>[2, -1, -1]</td></tr><tr><td>7</td><td>[7, 0, 0]</td><td>A</td><td>[0, 0, 0]</td></tr></tbody></table><p>如上，经过平滑性处理后，得到的服务器序列为 [A, A, B, A, C, A, A]，相比之前的序列 [A, A, A, A, A, B, C]，分布性要好一些。初始情况下 currentWeight = [0, 0, 0]，第7个请求处理完后，currentWeight 再次变为 [0, 0, 0]。</p><p>以上就是平滑加权轮询的计算过程，接下来，我们来看看 Dubbo-2.6.5 是如何实现上面的计算过程的。</p><div class=highlight><pre tabindex=0 style=color:#93a1a1;background-color:#002b36;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java><span style=display:flex><span><span style=color:#268bd2>public</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>RoundRobinLoadBalance</span> <span style=color:#268bd2>extends</span> AbstractLoadBalance { |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>final</span> String NAME <span style=color:#719e07>=</span> <span style=color:#2aa198>"roundrobin"</span>; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#268bd2>static</span> <span style=color:#dc322f>int</span> RECYCLE_PERIOD <span style=color:#719e07>=</span> 60000; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>protected</span> <span style=color:#268bd2>static</span> <span style=color:#268bd2>class</span> <span style=color:#268bd2>WeightedRoundRobin</span> { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 服务提供者权重</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#dc322f>int</span> weight; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 当前权重</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> AtomicLong current <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> AtomicLong(0); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 最后一次更新时间</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> <span style=color:#dc322f>long</span> lastUpdate; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#dc322f>void</span> <span style=color:#268bd2>setWeight</span>(<span style=color:#dc322f>int</span> weight) { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>this</span>.weight <span style=color:#719e07>=</span> weight; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 初始情况下，current = 0</span> |
| </span></span><span style=display:flex><span> current.set(0); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#dc322f>long</span> <span style=color:#268bd2>increaseCurrent</span>() { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// current = current + weight；</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> current.addAndGet(weight); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>public</span> <span style=color:#dc322f>void</span> <span style=color:#268bd2>sel</span>(<span style=color:#dc322f>int</span> total) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// current = current - total;</span> |
| </span></span><span style=display:flex><span> current.addAndGet(<span style=color:#719e07>-</span>1 <span style=color:#719e07>*</span> total); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 嵌套 Map 结构，存储的数据结构示例如下：</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// {</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// "UserService.query": {</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// "url1": WeightedRoundRobin@123, </span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// "url2": WeightedRoundRobin@456, </span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// },</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// "UserService.update": {</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// "url1": WeightedRoundRobin@123, </span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// "url2": WeightedRoundRobin@456,</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// }</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// }</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 最外层为服务类名 + 方法名，第二层为 url 到 WeightedRoundRobin 的映射关系。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 这里我们可以将 url 看成是服务提供者的 id</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> ConcurrentMap<span style=color:#719e07><</span>String, ConcurrentMap<span style=color:#719e07><</span>String, WeightedRoundRobin<span style=color:#719e07>>></span> methodWeightMap <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> ConcurrentHashMap<span style=color:#719e07><</span>String, ConcurrentMap<span style=color:#719e07><</span>String, WeightedRoundRobin<span style=color:#719e07>>></span>(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 原子更新锁</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>private</span> AtomicBoolean updateLock <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> AtomicBoolean(); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>@Override</span> |
| </span></span><span style=display:flex><span> <span style=color:#268bd2>protected</span> <span style=color:#719e07><</span>T<span style=color:#719e07>></span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> <span style=color:#268bd2>doSelect</span>(List<span style=color:#719e07><</span>Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>>></span> invokers, URL url, Invocation invocation) { |
| </span></span><span style=display:flex><span> String key <span style=color:#719e07>=</span> invokers.get(0).getUrl().getServiceKey() <span style=color:#719e07>+</span> <span style=color:#2aa198>"."</span> <span style=color:#719e07>+</span> invocation.getMethodName(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取 url 到 WeightedRoundRobin 映射表，如果为空，则创建一个新的</span> |
| </span></span><span style=display:flex><span> ConcurrentMap<span style=color:#719e07><</span>String, WeightedRoundRobin<span style=color:#719e07>></span> map <span style=color:#719e07>=</span> methodWeightMap.get(key); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (map <span style=color:#719e07>==</span> <span style=color:#cb4b16>null</span>) { |
| </span></span><span style=display:flex><span> methodWeightMap.putIfAbsent(key, <span style=color:#719e07>new</span> ConcurrentHashMap<span style=color:#719e07><</span>String, WeightedRoundRobin<span style=color:#719e07>></span>()); |
| </span></span><span style=display:flex><span> map <span style=color:#719e07>=</span> methodWeightMap.get(key); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> totalWeight <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>long</span> maxCurrent <span style=color:#719e07>=</span> Long.MIN_VALUE; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 获取当前时间</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>long</span> now <span style=color:#719e07>=</span> System.currentTimeMillis(); |
| </span></span><span style=display:flex><span> Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> selectedInvoker <span style=color:#719e07>=</span> <span style=color:#cb4b16>null</span>; |
| </span></span><span style=display:flex><span> WeightedRoundRobin selectedWRR <span style=color:#719e07>=</span> <span style=color:#cb4b16>null</span>; |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 下面这个循环主要做了这样几件事情：</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 1. 遍历 Invoker 列表，检测当前 Invoker 是否有</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 相应的 WeightedRoundRobin，没有则创建</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 2. 检测 Invoker 权重是否发生了变化，若变化了，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 则更新 WeightedRoundRobin 的 weight 字段</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 3. 让 current 字段加上自身权重，等价于 current += weight</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 4. 设置 lastUpdate 字段，即 lastUpdate = now</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 5. 寻找具有最大 current 的 Invoker，以及 Invoker 对应的 WeightedRoundRobin，</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 暂存起来，留作后用</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 6. 计算权重总和</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>for</span> (Invoker<span style=color:#719e07><</span>T<span style=color:#719e07>></span> invoker : invokers) { |
| </span></span><span style=display:flex><span> String identifyString <span style=color:#719e07>=</span> invoker.getUrl().toIdentityString(); |
| </span></span><span style=display:flex><span> WeightedRoundRobin weightedRoundRobin <span style=color:#719e07>=</span> map.get(identifyString); |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>int</span> weight <span style=color:#719e07>=</span> getWeight(invoker, invocation); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (weight <span style=color:#719e07><</span> 0) { |
| </span></span><span style=display:flex><span> weight <span style=color:#719e07>=</span> 0; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 检测当前 Invoker 是否有对应的 WeightedRoundRobin，没有则创建</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (weightedRoundRobin <span style=color:#719e07>==</span> <span style=color:#cb4b16>null</span>) { |
| </span></span><span style=display:flex><span> weightedRoundRobin <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> WeightedRoundRobin(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 设置 Invoker 权重</span> |
| </span></span><span style=display:flex><span> weightedRoundRobin.setWeight(weight); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 存储 url 唯一标识 identifyString 到 weightedRoundRobin 的映射关系</span> |
| </span></span><span style=display:flex><span> map.putIfAbsent(identifyString, weightedRoundRobin); |
| </span></span><span style=display:flex><span> weightedRoundRobin <span style=color:#719e07>=</span> map.get(identifyString); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// Invoker 权重不等于 WeightedRoundRobin 中保存的权重，说明权重变化了，此时进行更新</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (weight <span style=color:#719e07>!=</span> weightedRoundRobin.getWeight()) { |
| </span></span><span style=display:flex><span> weightedRoundRobin.setWeight(weight); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 让 current 加上自身权重，等价于 current += weight</span> |
| </span></span><span style=display:flex><span> <span style=color:#dc322f>long</span> cur <span style=color:#719e07>=</span> weightedRoundRobin.increaseCurrent(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 设置 lastUpdate，表示近期更新过</span> |
| </span></span><span style=display:flex><span> weightedRoundRobin.setLastUpdate(now); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 找出最大的 current </span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (cur <span style=color:#719e07>></span> maxCurrent) { |
| </span></span><span style=display:flex><span> maxCurrent <span style=color:#719e07>=</span> cur; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 将具有最大 current 权重的 Invoker 赋值给 selectedInvoker</span> |
| </span></span><span style=display:flex><span> selectedInvoker <span style=color:#719e07>=</span> invoker; |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 将 Invoker 对应的 weightedRoundRobin 赋值给 selectedWRR，留作后用</span> |
| </span></span><span style=display:flex><span> selectedWRR <span style=color:#719e07>=</span> weightedRoundRobin; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 计算权重总和</span> |
| </span></span><span style=display:flex><span> totalWeight <span style=color:#719e07>+=</span> weight; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 对 <identifyString, WeightedRoundRobin> 进行检查，过滤掉长时间未被更新的节点。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 该节点可能挂了，invokers 中不包含该节点，所以该节点的 lastUpdate 长时间无法被更新。</span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 若未更新时长超过阈值后，就会被移除掉，默认阈值为60秒。</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (<span style=color:#719e07>!</span>updateLock.get() <span style=color:#719e07>&&</span> invokers.size() <span style=color:#719e07>!=</span> map.size()) { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (updateLock.compareAndSet(<span style=color:#cb4b16>false</span>, <span style=color:#cb4b16>true</span>)) { |
| </span></span><span style=display:flex><span> <span style=color:#719e07>try</span> { |
| </span></span><span style=display:flex><span> ConcurrentMap<span style=color:#719e07><</span>String, WeightedRoundRobin<span style=color:#719e07>></span> newMap <span style=color:#719e07>=</span> <span style=color:#719e07>new</span> ConcurrentHashMap<span style=color:#719e07><</span>String, WeightedRoundRobin<span style=color:#719e07>></span>(); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 拷贝</span> |
| </span></span><span style=display:flex><span> newMap.putAll(map); |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 遍历修改，即移除过期记录</span> |
| </span></span><span style=display:flex><span> Iterator<span style=color:#719e07><</span>Entry<span style=color:#719e07><</span>String, WeightedRoundRobin<span style=color:#719e07>>></span> it <span style=color:#719e07>=</span> newMap.entrySet().iterator(); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>while</span> (it.hasNext()) { |
| </span></span><span style=display:flex><span> Entry<span style=color:#719e07><</span>String, WeightedRoundRobin<span style=color:#719e07>></span> item <span style=color:#719e07>=</span> it.next(); |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (now <span style=color:#719e07>-</span> item.getValue().getLastUpdate() <span style=color:#719e07>></span> RECYCLE_PERIOD) { |
| </span></span><span style=display:flex><span> it.remove(); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 更新引用</span> |
| </span></span><span style=display:flex><span> methodWeightMap.put(key, newMap); |
| </span></span><span style=display:flex><span> } <span style=color:#719e07>finally</span> { |
| </span></span><span style=display:flex><span> updateLock.set(<span style=color:#cb4b16>false</span>); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>if</span> (selectedInvoker <span style=color:#719e07>!=</span> <span style=color:#cb4b16>null</span>) { |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 让 current 减去权重总和，等价于 current -= totalWeight</span> |
| </span></span><span style=display:flex><span> selectedWRR.sel(totalWeight); |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// 返回具有最大 current 的 Invoker</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> selectedInvoker; |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span> |
| </span></span><span style=display:flex><span> <span style=color:#586e75>// should not happen here</span> |
| </span></span><span style=display:flex><span> <span style=color:#719e07>return</span> invokers.get(0); |
| </span></span><span style=display:flex><span> } |
| </span></span><span style=display:flex><span>} |
| </span></span></code></pre></div><p>以上就是 Dubbo-2.6.5 版本的 RoundRobinLoadBalance，大家如果能够理解平滑加权轮询算法的计算过程，再配合代码中注释，理解上面的代码应该不难。</p><h2 id=3总结>3.总结</h2><p>本篇文章对 Dubbo 中的几种负载均衡实现进行了详细的分析，内容比较多，大家慢慢消化。理解负载均衡代码逻辑的关键之处在于对背景知识的理解，因此大家在阅读源码前，务必先了解每种负载均衡对应的背景知识。</p><div id=pre-footer><h2>反馈</h2><p class=feedback--prompt>此页是否对您有帮助？</p><button class="btn btn-primary mb-4 feedback--yes">是</button> |
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