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Bug #58510 Enormous fragmantation in comparison with previous version
Submitted: 2009-01-15 03:59 UTC Modified: 2009-04-05 23:33 UTC
From: dco at mail dot ru Assigned:
Status: No Feedback Package: APC (PECL)
PHP Version: 5_2 CVS-2009-01-15 (dev) OS: Solaris 10 64bit Intel
Private report: No CVE-ID: None
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From: dco at mail dot ru
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 [2009-01-15 03:59 UTC] dco at mail dot ru
Description:
------------
PHP 5.2.8

We use APC under heavy load (10000+ user entries (read\write), 600+ files). When we used APC 3.1.2 fragmentation was low (i.e. Fragmentation: 2.96% ( 5.0 MBytes out of 170.0 MBytes in 2231 fragments)  ). 

We switched to APC 3.1.2 and fragmentation had grown to 100% in several hours (Fragmentation: 100% ( 150.0 MBytes out of 150.0 MBytes in 9934 fragments) ).

Total APC cache size is 256 mb.

Reproduce code:
---------------
-

Expected result:
----------------
Expected fragmentation to be comparable with that of version 3.0.19

Actual result:
--------------
Fragmentation is 100%

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 [2009-01-16 00:14 UTC] rasmus@php.net
But are you actually seeing a performance impact?  The fragmentation calculation is a bit artificial and may need to be updated for 3.1.2 actually.
 [2009-01-22 14:31 UTC] dco at mail dot ru
Yes we saw a performance impact.

The fragmentation made the cache full, so it had to delete old data to store some new data. The thing is we relied on user data would not be deleted occasionally.
 [2009-02-03 23:11 UTC] gopalv82 at yahoo dot com
Are you running apc with multiple segments and shm?

I suspect the expunge could cause a ton of problems that way.
 [2009-03-02 15:33 UTC] shire@php.net
Any updates regarding Gopal's questions?  

Also, perhaps you can give us some details regarding the size of your user values and how often they are updated (if you can easily reproduce the behavior via script that would be fantastic of course and would really help us to fix this).  I'm assuming your user entries are churning the cache more than your files or is this not accurate?
 
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