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I have quite a bit of fragmentation. Is this a serious problem? How can I fix this? How can I make sure it doesn't happen again? Are there any other config recommendations for me? Thanks!

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Have you tried increasing apc.shm_size?

It controls the overall amount of RAM that APC needs. I'm pretty sure that, even though your apc.php output seems to show empty space, there would be less fragmentation if you increased the memory available to APC. I think the fragmentation occurs when APC has to remove things and replace them, so giving it more breathing room can reduce fragmentation.

I'm pretty sure that fragmentation is a problem and that you should try to fix it. It should be fairly easy to get it down below 1%, though I may be biased because our HTTP server as gigs of spare ram that I throw at APC.

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As far as I can tell the fragmentation does not matter my graph looks much worse than that one and we have no issue with it.

we have tried to tune APC before but it seems to make no difference. I would not worry about it.

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@Alistair Prestidge fragmentation sure a problem. It make your server slow. I experienced this matter. Even i used 800MB for apc but it still happen fragment.

After i must use config : apc.filters: filter files were cached on disk.

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