This has taken several hours of testing and fiddling to debug, but I think I've got to the bottom of it.

Here's my setup:
Memcache 1.2.5
Memcache Pecl 3.0.3
Memcache module 6.x-1.5

I'm not 100% hot on what the latest versions are, but guessing those aren't probably up to date, but that's not where the issue is...

Upon calling dmemcache_get, because I'm using the memcache extension, the following will be called to set the value in memcache:

$mc->set($full_key, $value, MEMCACHE_COMPRESSED, $exp);

In most cases this is fine, but seemingly, this fails if the $value is an integer; Strings, arrays and objects seem to work fine. Change the flags to 0 and suddenly integers can be stored.

This isn't a massive issue at first glance, because almost all the data stored by the drupal is a cache object, except for one type of data: The counters for the prefixes for cache flushing, they are plain vanilla integers. This basically has the side effect of making it impossible to flush the cache! The '.prefix.' . $cid value never gets set, and doesn't seem to get incremented either.

I'm just finishing up a patch to the module that will not attempt to store integers compressed and will post it shortly.

CommentFileSizeAuthor
#1 memcache-872338.patch1.2 KBsteven jones

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steven jones’s picture

steven jones commented
StatusFileSize
new memcache-872338.patch1.2 KB

Patch attached.

steven jones’s picture

steven jones commented

I should probably say, that this is probably a bug in Memcache or the Memcache PECL extension, and this is just a bit of a workaround.

jeremy’s picture

jeremy commented
Assigned: Unassigned » jeremy
Priority: Critical » Normal

Reminding myself to try and duplicate this later -- the specific issue described is now fixed with the new wildcard support (replacing the "prefixes" logic), however I'm curious as I did run into something similar earlier when I was testing and before I saw this issue.

catch’s picture

catch
he/him
Primary language English
commented

Bumping this one.

c960657’s picture

c960657 commented

It is a known limitation that $mc->increment() does not work with MEMCACHE_COMPRESSED, see http://php.net/manual/en/function.memcache-increment.php.

However, I was not able to reproduce the problem on my machine. The following code works without problems:

$memcache->set('dummy', 123, MEMCACHE_COMPRESSED, time() + 3600);
$memcache->increment('dummy', 3);
$memcache->increment('dummy', 5);
var_dump($memcache->get('dummy'));

Whether compression takes place or not may be related to the compression threshold, see
http://php.net/manual/en/memcache.setcompressthreshold.php. I don't know what the default value is, if it has not been specified using $mc->setCompressThreshold().

jeremy’s picture

jeremy commented
Status: Needs review » Postponed

I wrote a quick drush script to try and duplicate this, but found that a cache_set of an integer (1, 0, TRUE and FALSE) followed by a cache_get returns the correct value. I am using the Memcache PECL extension to test, per the original bug report.

Furthermore, the Simpletest suite does perform a test validating that we are able to set and then get an plain integer, and this test also succeeds.

I suspect this has been fixed in the PECL extension, as I see similar older bug reports here: http://php.tonnikala.org/manual/ru/function.memcache-set.php

I'm going to go ahead and mark this as fixed, noting that you should use the latest Memcache PECL extension with the Drupal memcache module.

jeremy’s picture

jeremy commented
Status: Postponed » Fixed

Trying again to mark it fixed...

Status: Fixed » Closed (fixed)

Automatically closed -- issue fixed for 2 weeks with no activity.

slashrsm’s picture

slashrsm commented
Version: 6.x-1.x-dev » 7.x-1.0
Status: Closed (fixed) » Active

Reopening this, as I ran into the same issue with 7.x-1.0.

It is pretty nasty bug, since it causes incorrect behaviour of wildcard flushes. I was flushing some cache item, but it was not flushed, since the wildcard flushing counter was not updated properly. It was a really hard one to debug....

I *think* that this also has something to do with PHP version, since I was trying with the following combinations:
- PHP 5.3.1, Memcache 3.0.6
- PHP 5.3.2, Memcache 3.0.4
- PHP 5.3.6, Memcache 3.0.5

The latter was working OK. First two had problems. When I applied a workaround suggested at http://www.php.net/manual/en/memcache.set.php#100971, thing started to work properly on all machines.

I think we should implement some workaround for this bug. We should at least document PHP/Memcache versions, that are required for this to work properly if not.

jeremy’s picture

jeremy commented
Issue summary: View changes
Status: Active » Fixed

The memcache module does specify minimum version requirements.

Status: Fixed » Closed (fixed)

Automatically closed - issue fixed for 2 weeks with no activity.