This configures the storage type of the global/inter-process SSL Session Cache. This cache is an optional facility which speeds up parallel request processing. For requests to the same server process (via HTTP keep-alive), OpenSSL already caches the SSL session information locally. But because modern clients request inlined images and other data via parallel requests (usually up to four parallel requests are common) those requests are served by different pre-forked server processes. Here an inter-process cache helps to avoid unnecessary session handshakes.

The following five storage types are currently supported:

• none

  This disables the global/inter-process Session Cache. This will incur a noticeable speed penalty and may cause problems if using certain browsers, particularly if client certificates are enabled. This setting is not recommended.

• nonenotnull

  This disables any global/inter-process Session Cache. However it does force OpenSSL to send a non-null session ID to accommodate buggy clients that require one.

• dbm:/path/to/datafile

  This makes use of a DBM hashfile on the local disk to synchronize the local OpenSSL memory caches of the server processes. This session cache may suffer reliability issues under high load. To use this, ensure that mod_socache_dbm is loaded.

• shmcb:/path/to/datafile [ ( size ) ]

  This makes use of a high-performance cyclic buffer (approx. size bytes in size) inside a shared memory segment in RAM (established via /path/to/datafile ) to synchronize the local OpenSSL memory caches of the server processes. This is the recommended session cache. To use this, ensure that mod_socache_shmcb is loaded.

• dc:UNIX:/path/to/socket

  This makes use of the distcache distributed session caching libraries. The argument should specify the location of the server or proxy to be used using the distcache address syntax; for example, UNIX:/path/to/socket specifies a UNIX domain socket (typically a local dc_client proxy); IP:server.example.com:9001 specifies an IP address. To use this, ensure that mod_socache_dc is loaded.

Examples

SSLSessionCache "dbm:/usr/local/apache/logs/ssl_gcache_data"
SSLSessionCache "shmcb:/usr/local/apache/logs/ssl_gcache_data(512000)"

The ssl-cache mutex is used to serialize access to the session cache to prevent corruption. This mutex can be configured using the Mutex directive.