Hi,
At one wiki host there is 5.3.3-7+squeeze14 with apc 3.1.3p1 (both are quite old however
these are provided by Debian and I am not a regular admin of the server).
The wiki host has about 10-20k visits per day and about 3500 of pages. It's not the
smallest wiki.
There is apc.ini (already tweaked in hope to get a better utilization but no avail):
extension=apc.so
apc.enabled=1
apc.shm_segments= 1
apc.shm_size= 256
apc.ttl= 0 ; 7200
apc.user_ttl = 0 ; 7200
apc.gc_ttl = 0 ; 7200 ; was: none
apc.num_files_hint = 0; 1024
apc.user_entries_hint = 10000 ; was: none
apc.mmap_file_mask = /tmp/apc.XXXXXX
apc.enable_cli = 0 ; 1
apc.cache_by_default = 1
apc.max_file_size = 10M
apc.stat = 1; 0
apc.write_lock = 1 ; was: none
apc.localcache = 1 ; was: none
apc.localcache.size = 256 ; was: none
Part of LocalSettings.php (tried both CACHE_ACCEL constant and 'apc' string key
without any difference):
$wgMainCacheType = CACHE_ACCEL; # 'apc';
$wgMessageCacheType = CACHE_ACCEL; # 'apc';
$wgParserCacheType = CACHE_ACCEL; # 'apc';
However, apc.php monitoring script shows really low user cache usage which goes between
100K and 4M in about 20-30 seconds of time.
My actions:
1. I set all apc*ttl settings to zero in hope entries would not be timed out from cache.
2. I set apc.user_entries_hint = 10000 in suspect that MediaWiki may write a lot of
entries, thus older apc user cache entries are purged out.
3. I disabled all extensions except of Cite / ParserFunctions in suspect that some of them
might purge client cache or parser cache.
LocalSettings.php does NOT have $wgEnableParserCache = false;
4. I switched from custom skin to standard 1.19.2 Vector skin.
Nothing made any difference, user cache utilization is still very low after about a hour
of apache restart.
There are some client JS scripts, maybe I should try to disable these as well?
I tried to place debug calls into APCBagOStuff. MediaWiki seems to almost never calls
->delete(), a lots of ->set() and ->get().
Parser cache entries with 'pcache:idhash' keys have ttl of 86400 seconds, which
should be sufficient enough to fill 256MB of apc user cache.
Why the user cache is so low and why about every 10-30 seconds it loses lots of entries,
reducing from 4MB to 100K in apc.php monitoring script? Even if users were visiting only
few of 3500 pages, there should not be such cache drop.
Dmitriy