When added a memcached instance you can now select whether the cache is
being shared by other applications. The setting will determine the
purging strategy.
Shared caches will have individual keys deleted while dedicated caches
will have the entire cache purged (better performance over networks).
Note: This option only works with the correct version of the php
memcached extension and with the multi-site safe changes.
For stores where there is a very high rate of sets compared to gets, it
is beneficial to retrieve from the local server, skipping the network
overhead, at the expense of having to set many severs when a key is set.
This patch adds a memcached option to enable clustering. When on, only
one "server" is allowed, which will be where fetches are from, while
sets/updates/deletes/purges will occur to the all the servers in the
"set server" list.
To run unit tests, define TEST_CACHESTORE_MEMCACHED_TESTSERVERS with
multiple (return delimited) servers.
Various reasons can lead to the cache stores not being available
(missing extension, configuration...). Under those situations
the test must be skipped because for sure it will break if
we continue.
