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<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE manualpage SYSTEM "./style/manualpage.dtd">
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<manualpage metafile="socache.xml.meta">
<title>Shared Object Cache in Apache HTTP Server</title>
<summary>
<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>
</summary>
<section id="providers">
<title>Shared Object Cache Providers</title>
<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
<directive module="mod_cache_socache">CacheSocache</directive>,
<directive module="mod_authn_socache">AuthnCacheSOCache</directive>,
<directive module="mod_ssl">SSLSessionCache</directive>, and
<directive module="mod_ssl">SSLStaplingCache</directive>.</p>
<p>Currently available providers are:</p>
<dl>
<dt>"dbm" (<module>mod_socache_dbm</module>)</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" (<module>mod_socache_dc</module>)</dt>
<dd>This makes use of the <a href="http://distcache.sourceforge.net/">distcache</a>
distributed session caching libraries.</dd>
<dt>"memcache" (<module>mod_socache_memcache</module>)</dt>
<dd>This makes use of the <a href="http://memcached.org/">memcached</a>
high-performance, distributed memory object caching system.</dd>
<dt>"redis" (<module>mod_socache_redis</module>)</dt>
<dd>This makes use of the <a href="http://redis.io/">Redis</a>
high-performance, distributed memory object caching system.</dd>
<dt>"shmcb" (<module>mod_socache_shmcb</module>)</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>
</section>
</manualpage>
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