Shared Object Cache in Apache HTTP Server

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The Shared Object Cache provides a means to share simple data across all a server's workers, regardless of thread and process models. It is used where the advantages of sharing data across processes outweigh the performance overhead of inter-process communication.

Shared Object Cache Providers

The shared object cache as such is an abstraction. Four different modules implement it. To use the cache, one or more of these modules must be present, and configured.

The only configuration required is to select which cache provider to use. This is the responsibility of modules using the cache, and they enable selecton using directives such as AuthnCacheSOCache, SSLSessionCache, and SSLStaplingCache.

Currently available providers are:

"dbm" (mod_socache_dbm): This makes use of a DBM hash file. The choice of underlying DBM configuration may be configurable if the installed APR version supports multiple DBM implementations.
"dc" (mod_socache_dc): This makes use of the distcache distributed session caching libraries.
"mc" (mod_socache_memcache): This makes use of the memcached high-performance, distributed memory object caching system.
"shmcb" (mod_socache_shmcb): This makes use of a high-performance cyclic buffer inside a shared memory segment.