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MDL-37145 caching: noted recommendation for dedicated memcache servers

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Several reports have been made about the unexpected purging of entire
memcached servers when MUC is configured to use Memcache and caches
get purged.
This is expected and occurs because the memcache extenions don't
provide isolated containers. Moodle data is stored along side any other
data in the cache and when caches get purged all data gets removed
whether it belongs to Moodle or not.

The docs cover this point and here I've added notes about this to both
config-dist.php and cache/README.md
This commit is contained in:
Sam Hemelryk
2014-06-23 11:02:48 +12:00
parent 9663e6f8a5
commit d57563edd6
2 changed files with 9 additions and 0 deletions
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cache/README.md
Vendored
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@@ -246,3 +246,7 @@ The following snippet illustates how to configure the three core cache stores th
define('TEST_CACHESTORE_MEMCACHE_TESTSERVERS', '127.0.0.1:11211');
define('TEST_CACHESTORE_MEMCACHED_TESTSERVERS', '127.0.0.1:11211');
define('TEST_CACHESTORE_MONGODB_TESTSERVER', 'mongodb://localhost:27017');
Please be aware that if you are using Memcache or Memcached it is recommended to use dedicated Memcached servers.
When caches get purged the memcached servers you have configured get purged, any data stored within them whether it belongs to Moodle or not will be removed.
If you are using Memcached for sessions as well as caching/testing and caches get purged your sessions will be removed prematurely and users will be need to start again.
config-dist.php
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@@ -240,6 +240,11 @@ $CFG->admin = 'admin';
// $CFG->session_memcached_acquire_lock_timeout = 120;
// $CFG->session_memcached_lock_expire = 7200; // Ignored if memcached extension <= 2.1.0
//
// Please be aware that when selecting either Memcached or Memcache for sessions that it is advised to use a dedicated
// memcache server. The memcache and memcached extensions do not provide isolated environments for individual uses.
// Using the same server for other purposes (MUC for example) can lead to sessions being prematurely removed should
// the other uses of the server purge the cache.
//
// Following setting allows you to alter how frequently is timemodified updated in sessions table.
// $CFG->session_update_timemodified_frequency = 20; // In seconds.
//