Target percentage limit for APC fragmentation

Question

I've seen systems running happily with APC reporting < 10% fragmentation. I know as fragmentation increases performance decreases as APC needs to shuffle things around to find space.

Does anyone have a good rule of thumb as to the percentage of fragmetation you should keep APC below before you can expect overall performance to starts falling off significantly?

If so, at this point, is it a gradual linear drop of performance to fragmentation or does performance falling off a cliff?

What are you using APC for exactly? I have used it in few different scenarios. — Eduárd Moldován, Oct 17 '12 at 21:39
@EduárdMoldován we use it for both php opcode cache and user memory caching — Ray, Oct 17 '12 at 21:42
While at it, I found this: http://stackoverflow.com/questions/9292330/apc-cache-fragmentation-on-wordpress-site It might be helpful. — Eduárd Moldován, Oct 17 '12 at 21:48

Ray · Accepted Answer · 2012-12-30T15:21:17.887

Apparently no one knows... I've searched extensively and this is a very 'fuzzy' topic. I can't find benchmarks or tests anywhere regarding this. Just a lot of 'gee, you don't want a lot of fragmentation', without quantifying what 'a lot' means.

I'm going to stick with my gut percentage listed in the question, roughly < 10%.

Eventually, I'm going to run some benchmarks to gather some real data and see if my guess stands ups. I'll add them to this answer if I ever get the time to do them.

Target percentage limit for APC fragmentation

1 Answers1