Php – APC (Alternate PHP Cache) Throwing Lots of PHP Notices

I got APC 3.1.9 setup on my Linux box running PHP 5.3.6.

Caching works fine but I have noticed in our error logs, that APC throws a lot of PHP notices, such as:

[Wed Jun 29 01:08:56 2011] [error]
[client ip] PHP Notice:
require_once() [function.require-once]:
apc_cache_find [16085954]\n in
/path/to/file on line 75, referer:
/path/to/referer/file

[Wed Jun 29 01:08:56 2011] [error]
[client ip] PHP Notice:
require_once() [function.require-once]:
1. h->opened_path=[/path/to/file] h->filename=[/path/to/file]\n in
/path/to/file on line 84, referer:
/path/to/referer/file

[Wed Jun 29 01:08:56 2011] [error]
[client ip] PHP Notice: Unknown:
apc_cache_find [16215361]\n in Unknown
on line 0, referer:
/path/to/referer/file

–> /path/to/file & /path/to/referer/file have been inserted by me replacing the original file names

Any idea why APC throws all these messages ?