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| <h1 class="page">Distributed James Server — Performance checklist</h1> |
| <div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>This guide aims to help James operators refine their James configuration and set up to achieve better performance.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_database_setup"><a class="anchor" href="#_database_setup"></a>Database setup</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Cassandra, OpenSearch, RabbitMQ is a large topic in itself that we do not intend to cover here. Yet, here are some |
| very basic recommendation that are always beneficial to keep in mind.</p> |
| </div> |
| <div class="paragraph"> |
| <p>We recommend:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Running Cassandra, OpenSearch on commodity hardware with attached SSD. SAN disks are known to cause performance |
| issues for these technologies. HDD disks are to be banned for these performance related applications.</p> |
| </li> |
| <li> |
| <p>We recommend getting an Object Storage SaaS offering that suites your needs. Most generalist S3 offers will suite |
| James needs.</p> |
| </li> |
| <li> |
| <p>We do provide a guide on xref:[Database benchmarks] that can help identify and fix issues.</p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_james_configuration"><a class="anchor" href="#_james_configuration"></a>James configuration</h2> |
| <div class="sectionbody"> |
| <div class="sect2"> |
| <h3 id="_cassandra"><a class="anchor" href="#_cassandra"></a>Cassandra</h3> |
| <div class="paragraph"> |
| <p>People tunning for performance would likely accept relaxing their consistency needs. James allows doing this.</p> |
| </div> |
| <div class="paragraph"> |
| <p><strong>LightWeight Transactions (LWT)</strong> can be disabled where they are not essential. This can be done within |
| xref:[cassandra.properties]:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>mailbox.read.strong.consistency=false |
| message.read.strong.consistency=false |
| message.write.strong.consistency.unsafe=false |
| mailrepository.strong.consistency=false</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Also, James allows for <strong>Read repairs</strong> where consistency checks are piggy backed on reads randomly. This of course |
| comes at a performance cost as it generates extre reads, thus minimizing read repair probability can help improving |
| performance. This can be done within |
| xref:[cassandra.properties]:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>mailbox.read.repair.chance=0.00 |
| mailbox.counters.read.repair.chance.max=0.000 |
| mailbox.counters.read.repair.chance.one.hundred=0.000</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>One can also avoid some Cassandra requests by disabling ACLs (meaning users will only access to the mailboxes they own, |
| all mailbox-sharing features will thus not be achievable). This can be done within |
| xref:[cassandra.properties]:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>acl.enabled=false</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Important settings in the `` file includes:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Throttling: if too low then the Cassandra cluster is under-utilized. If too high, request bursts can cause significant |
| Cassandra overload.</p> |
| </li> |
| </ul> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre> advanced.throttler { |
| class = org.apache.james.backends.cassandra.utils.LockLessConcurrencyLimitingRequestThrottler |
| |
| max-queue-size = 10000 |
| |
| max-concurrent-requests = 192 |
| }</pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_object_storage"><a class="anchor" href="#_object_storage"></a>Object storage</h3> |
| <div class="paragraph"> |
| <p>We recommend the use of the blob store cache, which will be populated by email headers which shall be treated as metadata.</p> |
| </div> |
| <div class="paragraph"> |
| <p><code>blob.properties</code>:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>cache.enable=true |
| cache.cassandra.ttl=1year |
| cache.sizeThresholdInBytes=16 KiB</pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_rabbitmq"><a class="anchor" href="#_rabbitmq"></a>RabbitMQ</h3> |
| <div class="paragraph"> |
| <p>We recommend against the use of the CassandraMailQueueView, as browsing and advanced queue management features |
| is unnecessary for Mail Delivery Agent and are not meaningful in the absence of delays.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Similarly, we recommend turning off queue size metrics, which are expensive to compute.</p> |
| </div> |
| <div class="paragraph"> |
| <p>We also recommend against the use of publish confirms, which comes at a high performance price.</p> |
| </div> |
| <div class="paragraph"> |
| <p>In <code>rabbitmq.properties</code>:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>cassandra.view.enabled=false |
| |
| mailqueue.size.metricsEnabled=false |
| |
| event.bus.publish.confirm.enabled=false |
| mailqueue.publish.confirm.enabled=false</pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_jmap_protocol"><a class="anchor" href="#_jmap_protocol"></a>JMAP protocol</h3> |
| <div class="paragraph"> |
| <p>If you are not using JMAP, disabling it will avoid you the cost of populating related projections and thus is recommended. |
| Within <code>jmap.properties</code>:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>enabled=false</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>We recommend turning on EmailQueryView as it enables resolution of mailbox listing against Cassandra, thus unlocking massive |
| stability / performance gains. Within <code>jmap.properties</code>:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>view.email.query.enabled=true</pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_imap_smtp"><a class="anchor" href="#_imap_smtp"></a>IMAP / SMTP</h3> |
| <div class="paragraph"> |
| <p>We recommend against resolving client connection DNS names. This behaviour can be disabled via a system property within |
| <code>jvm.properties</code>:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>james.protocols.mdc.hostname=false</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Concurrent IMAP request count is the critical setting. In <code>imapServer.xml</code>:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre><concurrentRequests>200</concurrentRequests> |
| <maxQueueSize>4096</maxQueueSize></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Other recommendation includes avoiding unecessary work upon IMAP IDLE, not starting dedicated BOSS threads:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre><ignoreIDLEUponProcessing>false</ignoreIDLEUponProcessing> |
| <bossWorkerCount>0</bossWorkerCount></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_other_generic_recommendations"><a class="anchor" href="#_other_generic_recommendations"></a>Other generic recommendations</h3> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Remove unneeded listeners / mailets</p> |
| </li> |
| <li> |
| <p>Reduce duplication of Matchers within mailetcontainer.xml</p> |
| </li> |
| <li> |
| <p>Limit usage of "DEBUG" loglevel. INFO should be more than decent in most cases.</p> |
| </li> |
| <li> |
| <p>While GC tunning is a science in itself, we had good results with G1GC and a low pause time:</p> |
| </li> |
| </ul> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>-Xlog:gc*:file=/root/gc.log -XX:MaxGCPauseMillis=20 -XX:ParallelGCThreads=2</pre> |
| </div> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>We recommand tunning bach sizes: <code>batchsizes.properties</code>. This allows, limiting parallel S3 reads, while loading many |
| messages concurrently on Cassandra, and improves IMAP massive operations support.</p> |
| </li> |
| </ul> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>fetch.metadata=200 |
| fetch.headers=30 |
| fetch.body=30 |
| fetch.full=30 |
| |
| copy=8192 |
| |
| move=8192</pre> |
| </div> |
| </div> |
| </div> |
| </div> |
| </div> |
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