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Bug #58156 APC does not cache anymore some files
Submitted: 2008-04-15 04:31 UTC Modified: 2008-06-26 08:15 UTC
From: laurent dot baillet at gmail dot com Assigned:
Status: Closed Package: APC (PECL)
PHP Version: 5.2.5 OS: Linux Debian Etch (up-to-date)
Private report: No CVE-ID: None
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From: laurent dot baillet at gmail dot com
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 [2008-04-15 04:31 UTC] laurent dot baillet at gmail dot com 
Description:
------------
Hello

For some reason, after an upgrade, my setup based on apache 1 (1.3.34-4.1+etch1), PHP 5.2.5 as an Apache module and APC 3.0.18 ceased to work :
- the load becomes really high
- some files are not cached anymore 

Apache has never evolved in the scenario so let's concentrate on PHP and APC.

- PHP 5.2.1 + APC 3.0.16 (APC generated with this PHP version) : worked
- PHP 5.2.1 + APC 3.0.18 (APC generated with this PHP version) : worked
- PHP 5.2.5 + APC 3.0.18 (APC generated on a  PHP 5.2.1 + APC 3.0.18 box) : worked
- PHP 5.2.5 + APC 3.0.18 (APC generated with this PHP version) : broken

Broken means that a large part of files that should be cached are not cached anymore

Here is the config part (it did not change) :

extension=apc.so
apc.enabled=1
apc.optimization=0
apc.ttl=300
apc.shm_size=64
apc.shm_segments=1
apc.num_files_hint=3500
apc.user_entries_hint=0
apc.mmap_file_mask=/tmp/apc.XXXXXX
apc.file_update_protection=0
apc.slam_defense=90
apc.filters="generes,tmp"


Reproduce code:
---------------
Just start Apache and wait for the mess

Expected result:
----------------
Most obviously, the auto_prepend file included on all pages is not cached anymore. Other files neither, leading to very high load.

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 [2008-04-17 09:38 UTC] laurent dot baillet at gmail dot com 
edit : it could be related to my LFS_CFLAGS

having removed "-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64" from inclusion in the compilation process, it seems to work fine.

under investigation
 [2008-06-26 08:15 UTC] gopalv82 at yahoo dot com 
3.0.16 called stat() directly

3.0.18 called php's internal url_stat()

If the php build and apc build differs in off_t sizes (i.e _FILE_OFFSET_BITS), the size of "struct stat" will vary between 88 and 96 bytes, thus giving you the wrong value in the struct members (as read by APC).

I'm writing a dwarf2 tool (ala lkml's pahole) to scan for this kind of stuff (about the sixth time I've seen this in 3 months) but don't hold your breath :)
 
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