OMcache is a C and Python library for accessing memcached servers. The goals of the OMcache project are a stable API and ABI and 'easy' integration into complex applications and systems. OMcache is meant to be used as a middleware layer to provide redundancy and consistency to a memcached server cluster. OMcache specifically tries to avoid ABI breakage and does not mask any signals or call blocking functions to help integrating it into other solutions.
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OMcache has been developed and tested on x86-64 Linux, but it should work on other Linux architectures as well as Mac OS X on x86 and Solaris on Sparc without any changes. Other platforms will probably require some changes.
OMcache can be built with recent versions of GCC and Clang. Clang and GCC versions prior to 4.9 will emit some spurious warnings about missing field initializers. Asynchronous name lookups require the libasyncns library; OMcache can be built without it by passing WITHOUT_ASYNCNS=1 argument to make, but that will cause name lookups to become blocking operations.
Unit tests are implemented using the Check unit testing framework. Check version 0.9.10 or newer is recommended, earlier versions can be used but their log output is limited.
The Python module requires CFFI 0.6+ and supports CPython 2.6, 2.7 and 3.3+ and PyPy 2.2+.
OMcache tries to be compatible with libmemcached where possible. During normal operations where all servers are available and no failovers have happened the two memcache clients should always select the same servers for keys. Libmemcached's failover mechanism has traditionally been poorly documented and its details have changed occasionally between the releases so 100% compatibility is not possible.
OMcache supports configurable key distribution algorithms, the default is
the one used by libmemcached version 1.0.10 and newer, called
omcache_dist_libmemcached_ketama in OMcache. Libmemcached versions
prior to 1.0.10 had a bug in the implementation of the algorithm which
caused it to use a mix of the normal ketama and weighted ketama, using
Jenkins hashing for keys and md5 hashing for hosts. OMcache supports this
algorithm as omcache_dist_libmemcached_ketama_pre1010.
OMcache also provides a thin API compatibility wrapper header which allows simple applications to be converted to use OMcache instead of libmemcached by including "omcache_libmemcached.h" instead of "libmemcached/memcached.h". Similarly there's a compatibility layer for pylibmc in omcache_pylibmc.py which provides a limited pylibmc-like API for OMcache.
The functionality provided by these wrappers is limited and they are not supported, they're provided to make it easy to test OMcache in simple programs that use the libmemcached and pylibmc APIs.
OMcache is released under the Apache License, Version 2.0.
For the exact license terms, see LICENSE and http://opensource.org/licenses/Apache-2.0 .
OMcache was created by Oskari Saarenmaa <[email protected]> and is maintained by Ohmu Ltd's hackers <[email protected]>.
F-Secure Corporation provided the infrastructure for testing OMcache in its initial development process and contributed to the pylibmc and libmemcached compatibility layers as well as ported pgmemcache (PostgreSQL memcached interface) to run on OMcache.
MD5 implementation is based on Solar Designer's Public Domain / BSD licensed code from openwall.info.
Bug reports and patches are very welcome, please post them as GitHub issues and pull requests at https://github.com/ohmu/omcache