APC缓存碎片问题

Question

I'm running APC (php cache) on a medium website (13 000 visits a day) on a CentOS server 5 running php 5.3.3 with APC 3.1.4 with 4Gb of RAM. In the last weeks I'm experiencing many " unable to allocate memory for pool " errors in logs, and often the site goes down.

I think the problem is in APC. From the stats I see that the cache is full after an hour or two, and the fragmentation always jumps to 100%. This are my config settings of apc.ini:

apc.cache_by_default    1
apc.canonicalize    0
apc.coredump_unmap  0
apc.enable_cli  0
apc.enabled 1
apc.file_md5    0
apc.file_update_protection  2
apc.filters 
apc.gc_ttl  3600
apc.include_once_override   0
apc.lazy_classes    00
apc.lazy_functions  0
apc.max_file_size   1M
apc.mmap_file_mask  /dev/zero
apc.num_files_hint  0
apc.preload_path    
apc.report_autofilter   0
apc.rfc1867 0
apc.rfc1867_freq    0
apc.rfc1867_name    APC_UPLOAD_PROGRESS
apc.rfc1867_prefix  upload_
apc.rfc1867_ttl 3600
apc.shm_segments    1
apc.shm_size    512M
apc.slam_defense    1
apc.stat    1
apc.stat_ctime  0
apc.ttl 7200
apc.use_request_time    1
apc.user_entries_hint   0
apc.user_ttl    7200
apc.write_lock  1

From APC stats I can see that the number of cached files is very high (40 000), and this is due to the plethora of cache files of phpbb and mediawiki. Do I have to prevent APC caching this files using apc.filters ? Are there solutions to the problem?

Answer 1

You really should set apc.stat=0 on your production server and it will prevent APC from actually going to the IO to check if the file has been changed.

also set apc.slam_defense=0 as it's deprecated

Check out documentation for other options: http://php.net/manual/en/apc.configuration.php

Answer 2

I think you should set apc.mmap_file_mask = /tmp/apc-yourusernamehere.XXXXXX for file-backed mmap; make file mask unique by adding your unique string; XXXXXX (exactly 6 X's) must remain to allow APC to add random string OR set to /dev/zero for anonymous mmap if you can spare the memory.

I can see that you are using /dev/zero which takes memory unnecessarily.