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From Ted Keller <kel...@bfg.com>
Subject mod_proxy/4401: Multiple Proxy Cache Garbage Collections in Operation
Date Wed, 12 May 1999 21:31:05 GMT

>Number:         4401
>Category:       mod_proxy
>Synopsis:       Multiple Proxy Cache Garbage Collections in Operation
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Wed May 12 14:40:01 PDT 1999
>Originator:     keller@bfg.com
>Release:        1.3.6
IRIX d8544-cs 5.3 11091810 IP7 mips

Gcc 2.8.1
We've detected daily several copies of apache running in garbage collection mode
simultaneously.  Usually, one copy will be executed, then exactly 6 hours later
several additional copies will be started and will start garbage collection activities.
None of these copies seems to be aware of the others, so they continue to initiate
and start their own garbage collection processes.

This severly impacts proxy server performance.  

dbx(1) of one process reports...

root@d8544-cs 50: kill -STOP 21493
root@d8544-cs 51: dbx -p 21493
dbx version 3.19 Nov  3 1994 19:59:46
Process 21493 (httpd) stopped at [_open:15 +0x8,0xfacad6c]
         Source (of open.s) not available for Process 21493
(dbx) where
>  0 _open(0x100a5b38, 0x0, 0x3, 0x0) ["open.s":15, 0xfacad6c]
   1 sub_garbage_coll() ["proxy_cache.c":1, 0x412438]

Key parameters in httpd.c are....

CacheRoot /scratch/internet/apache
CacheSize 800
CacheGcInterval 4 
CacheMaxExpire 6
CacheLastModifiedFactor 0.8
CacheDefaultExpire 4
# NoCache bfg.com
CacheForceCompletion 80

I have increased the CacheMaxExpire to 12 as a temporary fix????

Killing off unneeded processes returns system to normal perfornamce levels.



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