<!DOCTYPE html SYSTEM "about:legacy-compat">
<html lang="en"><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta content="width=device-width, initial-scale=1" name="viewport">
<!--
        XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
              This file is generated from xml source: DO NOT EDIT
        XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
      -->
<title>Shared Object Cache in Apache HTTP Server - Apache HTTP Server Version 2.4</title>
<link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet">
<link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size">
<link href="./style/css/manual-print.css" rel="stylesheet" media="print" type="text/css"><link rel="stylesheet" type="text/css" href="./style/css/prettify.css">
<script src="./style/scripts/prettify.min.js">
</script>

<link href="./images/favicon.png" rel="shortcut icon"></head>
<body id="manual-page" class="no-sidebar"><div id="page-header">
<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/quickreference.html">Directives</a> | <a href="https://cwiki.apache.org/confluence/display/httpd/FAQ">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a> | <a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2">Report a bug</a></p>
<p class="apache">Apache HTTP Server Version 2.4</p>
<img alt="" src="./images/feather.png"></div>
<div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif"></a></div>
<div id="path">
<a href="https://www.apache.org/">Apache</a> &gt; <a href="https://httpd.apache.org/">HTTP Server</a> &gt; <a href="https://httpd.apache.org/docs/">Documentation</a> &gt; <a href="./">Version 2.4</a></div><div id="page-content"><div id="preamble"><h1>Shared Object Cache in Apache HTTP Server</h1>
<button aria-label="Toggle language list" class="lang-toggle"><svg xmlns="http://www.w3.org/2000/svg" stroke-width="2" stroke="currentColor" fill="none" viewBox="0 0 24 24" height="16" width="16"><circle r="10" cy="12" cx="12"/><line y2="12" x2="22" y1="12" x1="2"/><path d="M12 2a15.3 15.3 0 0 1 4 10 15.3 15.3 0 0 1-4 10 15.3 15.3 0 0 1-4-10 15.3 15.3 0 0 1 4-10z"/></svg></button>
<div class="toplang">
<p><span>Available Languages: </span><a href="./en/socache.html" title="English">&nbsp;en&nbsp;</a> |
<a href="./fr/socache.html" hreflang="fr" rel="alternate" title="Fran&ccedil;ais">&nbsp;fr&nbsp;</a></p>
</div>

    <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>
  </div>
<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif"></a></div>
<div class="section">
<h2 id="providers">Shared Object Cache Providers <a title="Permanent link" href="#providers" class="permalink">&para;</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>

  </div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="./en/socache.html" title="English">&nbsp;en&nbsp;</a> |
<a href="./fr/socache.html" hreflang="fr" rel="alternate" title="Fran&ccedil;ais">&nbsp;fr&nbsp;</a></p>
</div><div id="footer">
<p class="apache">Copyright 2026 The Apache Software Foundation.<br>Licensed under the <a href="https://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/quickreference.html">Directives</a> | <a href="https://cwiki.apache.org/confluence/display/httpd/FAQ">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a> | <a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2">Report a bug</a></p></div><script><!--//--><![CDATA[//><!--
if (typeof(prettyPrint) !== 'undefined') {
    prettyPrint();
}
var langToggle = document.querySelector('.lang-toggle');
var topLang = document.querySelector('.toplang');
if (langToggle && topLang) {
    langToggle.addEventListener('click', function() { topLang.classList.toggle('open'); });
}
var qv = document.getElementById('quickview');
if (qv) {
    document.body.appendChild(qv);
    var qvBtn = document.createElement('button');
    qvBtn.className = 'qv-toggle';
    qvBtn.setAttribute('aria-label', 'Toggle page navigation');
    qvBtn.innerHTML = '&#9776;';
    document.body.appendChild(qvBtn);
    qvBtn.addEventListener('click', function() {
        var isOpen = qv.classList.toggle('open');
        if (isOpen) {
            qv.style.top = window.scrollY + 10 + 'px';
        }
    });
    window.addEventListener('scroll', function() { qv.classList.remove('open'); });
}
//--><!]]></script>
</body></html>