Support for storing sessions in memcache/redis

Here's a partial implementation of memcache sessions by Darrin at Catalyst Australia. This is just the session.php code switched to use memcache instead of file; a full implementation will require an admin interface (or at least a $cfg variable) to let the user switch between them.

Actually, yeah, a $cfg variable would probably be more appropriate for this than an admin screen. Especially since, if you change your session handler, your session is immediately killed and you're force-logged out.

Here's a branch on my personal gitorious repo that has this implementation: https://gitorious.org/mahara/agwells-mahara/source/79bda3f3d2da7b9b45333bf1d449eff5f94059d5:

That's 1.8_STABLE, with the initial memcache patch and a further commit that fixes a bug with session.gc_maxlifetime in that initial patch. We've been using these two patches on several production sites for the past couple of months without any problems.

As mentioned above, what we need in order to be able to upstream this, is a $cfg variable to allow the site admin to specify whether to use standard filesystem sessions, or memcache. Ideally, this would be a pluggable system to allow for further session types to be implemented, but at the minimum it'd be fine to just have it hard-coded to memcache or filesystem.

Hi Aaron;
Yes, It would be good to have session plugins. +1 for this

I've moved the "official" source of this patch to the Catalyst Github account. There are branches ending in "-memcache" for each Mahara version I've needed to port it to so far: https://github.com/catalyst/mahara/tree/mh1504-memcache

Patch for "master" branch: https://reviews.mahara.org/5378

Reviewed: https://reviews.mahara.org/5378
Committed: https://git.mahara.org/mahara/mahara/commit/bbd333b7a68cc727041762f5362612220caeaa19
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit bbd333b7a68cc727041762f5362612220caeaa19
Author: Robert Lyon <email address hidden>
Date: Fri Dec 23 11:36:07 2016 +1300

Bug 785469: Add support for memcached session save handler

Introduce new global setting:
$cfg->sessionhandler

behatnotneeded

Change-Id: I386c94c4d1ab06fbde110c705789f9dcfaaead67
Signed-off-by: Robert Lyon <email address hidden>

For Redis see bug #1747297