Installing and upgrading help

Help with Session and Request Cache configuration

 
Picture of Sharath Chandra Kogila
Help with Session and Request Cache configuration
 
I am using latest Moodle (3.3+)


I am planning to use MemCached for Application, Session and Request Data Caching. I have couple of questions regarding the same. Looking for some help  in configuration

Configuring Application Cache

I added Memcached Store Instance Successfully and also mapped the store instance to Application Chache. But i get the following tool tip error when i see the mapping from the configuration page (tool tip is shown on exclamation mark) 

"This store doesn't meet the requirements for all known definitions. Definitions for which this store is inadequate will be given the original default store instead of the selected store." 

Also, how does the config.php variables, $CFG->tempdir, $CFG->cachedir relate to above configuration. If i configure the application cache from Site Administration, should i enable these variables (actually i disabled them currently)


Configuring Session Cache

How do i configure Session Cache to use MemCached backend. Is it possible from Site Administration console  or config.php

Configuring Request Cache

How do i configure Request Cache to use MemCached backend. Is it possible from Site Administration console  or config.php

 

Thank you,

Sharath

 
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Picture of Benoît Lathière
Re: Help with Session and Request Cache configuration
 

hi! Sharath,

You did have any reply to your questions, so I will try to give you some explanations. But I'm not an expert.

Memcached engine can't support all types of cache in Moodle, because its mechanism is not "perfect". By example, Memcached doesn't have mocking system, so when Moodle want to cleanup sessions key in Memcached, Memcached drop all the cached vars, not just the ones from sessions!

From Moodle Admin page "Site administration > Plugins > Caching > Configuration". The installed extensions are listed ; in the "Supports" column, you can see which features the engine has. Redis and APCu are good choices.

I do that :

  • using Memcached for sessions (do the configuration in config.php (search at "Memcached session handler" in the file) ;
  • using a Redis server for Application Cache ;
  • I don't share caches between nodes from my cluster, so it's not a SPOF (https://en.wikipedia.org/wiki/Single_point_of_failure). The cache s not optimized to the maximum, but If my local Memcached server fails, others Virtual Machines continue to run.

I don't use settings "$CFG->tempdir" and "$CFG->cachedir".

I don't know how to configure Request Cache, because I don't know any engine for that!

Best regards,

Benoit.

 
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