The Postfix memcache client type allows you to hook up Postfix to a memcache server. This implementation supports multiple memcache servers for redundancy, and multiple memcache clients that you can use for different table lookups. The Postfix memcache client supports both lookup and update operations.
Typically, a memcache map is used to reduce query load on a database server, or to share a low-latency database among different Postfix instances.
The Postfix memcache client is based on libmemcache, which will terminate its process after a memcache server goes down. To avoid this, set up redundant memcache servers that have no common source of failure.
The Postfix memcache client cannot be used for security-sensitive tables such as alias_maps (these may contain "|command" and "/file/name" destinations), or virtual_uid_maps and virtual_gid_maps (these specify UNIX process privileges). Typically, a memcache database is shared via a TCP socket, and is writable not only by Postfix, but by any process that can talk to the memcache server.
The Postfix memcache client requires additional configuration when used with the postscreen(8) and verify(8) daemons. For details see the ttl parameter discussion in the memcache_table(5) manual page.
The Postfix memcache client is supported only with libmemcache version 1.4.0. Some libmemcache features are documented by reading libmemcache source code, instead of a proper API.
To build Postfix with memcache client support, specify -DHAS_MEMCACHE, the location of the libmemcache include files, and the location of the libmemcache object library.
% make -f Makefile.init makefiles \ 'CCARGS=-DHAS_MEMCACHE -I/usr/local/include' \ 'AUXLIBS=-L/usr/local/lib -lmemcache'
Then run 'make'.
If the build fails with "undefined reference to `mcm_buf_len'" (and with a similar error message for mcm_buf_remain_off), then you need to edit libmemcache source code.
The following instructions apply to libmemcache 1.4.0.rc2.
Open the libmemcache source file include/memcache/buffer.h.
Delete the "inline" words before the functions that were reported in the "undefined reference" error messages.
Recompile and reinstall libmemcache.
Then, continue building Postfix by running 'make'.
Configuration is described in the memcache_table(5) manpage.
The first memcache client for Postfix was written by Omar Kilani.
Wietse wrote a new memcache client from the ground up. Besides also using libmemcache, the current implementation bears no resemblance to Omar's work.