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From "Jerry Lam" <j...@sandvine.com>
Subject [users@httpd] Understanding Memory Usage Per Process
Date Tue, 05 Apr 2005 15:11:56 GMT
Hi,

I ran into a situation where I would like to understand how exactly memory is handled in apache
process. 
I'm using 1.3.33 apache on a freebsd box having 1GB or RAM. The box has only apache and postgresql
servers running. 
What I did is I ran a script on the command line which will take 180M of memory to finsih,
then I tried running the same script within apache by using mod_websh to serve the request.
The apache child process goes up to 200M (from the top command) and it never drops back to
its initial value even after the script is done. 
The script doesn't have memory leak. My understanding is that the mod_websh will run the tcl
interpreter and execute the script. After it is done, it kills the tcl interpreter and memory
should be returned back to the OS (I supposed). But it doesn't seem this is the case. I'm
sure the memory is not lock up. If I ran the same script over and over while true it within
the request, the memory usage stays exactly 200M even after some hours of execution within
the process. 

- Can someone explain this to me clearly what is happening here? I would like to know how
memory is allocated within apache? Though the only explanation I have is that mod_websh request
memory from apache, and apache assigns some blocks of memory to mod_websh after mod_websh
is done, it returns the memory back to apache (in this case 200M) but the memory is kept within
the process to serve the next request. Please add / modify / correct this explanation if you
think something not quite true about it. 

Thank you,


Jerry

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