Intermittent 500 errors with certain php code

[Adam Cooper]

Binary package hint: php-apc

Description: Ubuntu 10.04.1 LTS
Release: 10.04

php-apc:
  Installed: 3.1.3p1-2
  Candidate: 3.1.3p1-2
  Version table:
 *** 3.1.3p1-2 0
        500 http://us.archive.ubuntu.com/ubuntu/ lucid/universe Packages
        100 /var/lib/dpkg/status

I have a wordpress blog installed in a vhost on a VPS using the above APC package and the default php5.3 and apache2 packages that come with 10.04. On an intermittent basis accessing the /wp-admin path on the blog will return a 500 error - and will continue to return this error from that point onward. I am unable to access any paths under this directory and so management of the blog is impossible.

Restarting apache or clearing the op-code cache (via the apc.php file) will cause the error to disappear and I will be able to access the blog admin area from that point onward. The error will likely reoccur within the next 24hrs.

I am running a number of php websites and this is the only one to show any errors like this (that I have found). I am unable to find any indications of a problem in the log files. There are no entires in the error.log and only a single line with a 500 response code in the access.log. Syslog and /var/log/messages show no entries.

It looks to me like a corrupted cache of some kind but I don't know enough to say for sure. The blogs files and database were recently migrated from a 8.04 based VPS that had a pecl installed version of APC. It did not ever experience this issue.

[Adam Cooper (adam-j-cooper)]

Forgot to mention that the version of wordpress installed 3.0.3 (the latest as of this comment)

[Adam Cooper (adam-j-cooper)]

I have now installed the PECL version of APC (3.1.6) and have yet to encounter any issues. It has been running for 3 days now and I have not had to clear the opcode cache or restart apache. I would like have had to do this 2-3 times using the apt-get installed version of APC.