I recently saw some strange behavior on our PHP Servers.
We are using PHP-FPM 5.3.8 with APC 3.1.9. The apc.stat flag is turned off, so files should be read only once from the harddisk and then cached in memory. On every deployment we just clear APC.
Our code is using the symfony framework, which generates PHP files inside the /cache folder once the code get's executed for the first time. From then on it should read these PHP files in /cache to execute faster.
Our problem is that sometimes PHP tells us that certain files in /cache do not exist, but when I check manually I see that these files exist.
My suspicion is that APC with apc.stat off caches during the first request after each deployment that these files don't exist, and then remembers that these files don't exist instead of checking again. Actually they do exist at the time of the second request, because the first request generated them, only at the time of the first request they didn't.
Is it possible that APC with apc.stat off behaves that way? That it doesn't only cache existing files, but also which files do not exist?