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| <title>Shared Object Cache in Apache HTTP Server - Apache HTTP Server Version 2.5</title> |
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| <p class="apache">Apache HTTP Server Version 2.5</p> |
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| <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.5</a></div><div id="page-content"><div id="preamble"><h1>Shared Object Cache in Apache HTTP Server</h1> |
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| <p>The Shared Object Cache provides a means to share simple data |
| across all a server's workers, regardless of <a href="mpm.html">thread |
| and process models</a>. It is used where the advantages of sharing |
| data across processes outweigh the performance overhead of |
| inter-process communication.</p> |
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| <div class="section"> |
| <h2><a name="providers" id="providers">Shared Object Cache Providers</a> <a title="Permanent link" href="#providers" class="permalink">¶</a></h2> |
| |
| <p>The shared object cache as such is an abstraction. Five different |
| modules implement it. To use the cache, one or more of these modules |
| must be present, and configured.</p> |
| <p>The only configuration required is to select which cache provider |
| to use. This is the responsibility of modules using the cache, and |
| they enable selection using directives such as |
| <code class="directive"><a href="./mod/mod_cache_socache.html#cachesocache">CacheSocache</a></code>, |
| <code class="directive"><a href="./mod/mod_authn_socache.html#authncachesocache">AuthnCacheSOCache</a></code>, |
| <code class="directive"><a href="./mod/mod_ssl.html#sslsessioncache">SSLSessionCache</a></code>, and |
| <code class="directive"><a href="./mod/mod_ssl.html#sslstaplingcache">SSLStaplingCache</a></code>.</p> |
| <p>Currently available providers are:</p> |
| <dl> |
| <dt>"dbm" (<code class="module"><a href="./mod/mod_socache_dbm.html">mod_socache_dbm</a></code>)</dt> |
| <dd>This makes use of a DBM hash file. |
| The choice of underlying DBM used may be configurable |
| if the installed APR version supports multiple DBM implementations.</dd> |
| <dt>"dc" (<code class="module"><a href="./mod/mod_socache_dc.html">mod_socache_dc</a></code>)</dt> |
| <dd>This makes use of the <a href="http://distcache.sourceforge.net/">distcache</a> |
| distributed session caching libraries.</dd> |
| <dt>"memcache" (<code class="module"><a href="./mod/mod_socache_memcache.html">mod_socache_memcache</a></code>)</dt> |
| <dd>This makes use of the <a href="http://memcached.org/">memcached</a> |
| high-performance, distributed memory object caching system.</dd> |
| <dt>"redis" (<code class="module"><a href="./mod/mod_socache_redis.html">mod_socache_redis</a></code>)</dt> |
| <dd>This makes use of the <a href="http://redis.io/">Redis</a> |
| high-performance, distributed memory object caching system.</dd> |
| <dt>"shmcb" (<code class="module"><a href="./mod/mod_socache_shmcb.html">mod_socache_shmcb</a></code>)</dt> |
| <dd>This makes use of a high-performance cyclic buffer inside a |
| shared memory segment.</dd> |
| </dl> |
| |
| <p>The API provides the following functions:</p> |
| |
| <dl> |
| <dt>const char *create(ap_socache_instance_t **instance, const char *arg, |
| apr_pool_t *tmp, apr_pool_t *p);</dt> |
| <dd>Create a session cache based on the given configuration string. |
| The instance pointer returned in the instance parameter will be |
| passed as the first argument to subsequent invocations.</dd> |
| |
| <dt>apr_status_t init(ap_socache_instance_t *instance, const char *cname, |
| const struct ap_socache_hints *hints, |
| server_rec *s, apr_pool_t *pool)</dt> |
| <dd>Initialize the cache. The cname must be of maximum length 16 |
| characters, and uniquely identifies the consumer of the cache |
| within the server; using the module name is recommended, e.g. |
| "mod_ssl-sess". This string may be used within a filesystem |
| path so use of only alphanumeric [a-z0-9_-] characters is |
| recommended. If hints is non-NULL, it gives a set of hints for |
| the provider. Return APR error code.</dd> |
| |
| <dt>void destroy(ap_socache_instance_t *instance, server_rec *s)</dt> |
| <dd>Destroy a given cache instance object.</dd> |
| |
| <dt>apr_status_t store(ap_socache_instance_t *instance, server_rec *s, |
| const unsigned char *id, unsigned int idlen, |
| apr_time_t expiry, |
| unsigned char *data, unsigned int datalen, |
| apr_pool_t *pool)</dt> |
| <dd>Store an object in a cache instance.</dd> |
| |
| <dt>apr_status_t retrieve(ap_socache_instance_t *instance, server_rec *s, |
| const unsigned char *id, unsigned int idlen, |
| unsigned char *data, unsigned int *datalen, |
| apr_pool_t *pool)</dt> |
| <dd>Retrieve a cached object.</dd> |
| |
| <dt>apr_status_t remove(ap_socache_instance_t *instance, server_rec *s, |
| const unsigned char *id, unsigned int idlen, |
| apr_pool_t *pool)</dt> |
| <dd>Remove an object from the cache.</dd> |
| |
| <dt>void status(ap_socache_instance_t *instance, request_rec *r, int flags)</dt> |
| <dd>Dump the status of a cache instance for mod_status.</dd> |
| |
| <dt>apr_status_t iterate(ap_socache_instance_t *instance, server_rec *s, |
| void *userctx, ap_socache_iterator_t *iterator, |
| apr_pool_t *pool)</dt> |
| <dd>Dump all cached objects through an iterator callback.</dd> |
| </dl> |
| |
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