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From Ian Holsman <>
Subject Re: mod_deflate and load
Date Thu, 03 Jul 2003 17:23:52 GMT
Bill Marrs wrote:
> Ian,
I'm cross posting this to
> I had been a user of Apache 1.3 and mod_gzip, but I recently upgraded to 
> Apache 2.0 and I'm trying to use mod_deflate.
> I got it working fairly well, but it's causing high load and page 
> timeouts during peak periods of operation for my site.
> The output I'm compressing is generated from mod_perl scripts.
> mod_gzip had not had this problem.  It's possible that there are other 
> factors (the whole system was upgraded), so I can't absolutely blame 
> mod_deflate, but removing it certainly fixes the load problem.

sounds like a cpu load issue.

> I've been dropping the DeflateCompressionLevel, which seems to help, but 
> I'm already down to 2 and I'm still getting timeouts.

I find that surprising.. the reason I do is when I put it on one of our 
production machines we saw a 10% in cpu load, but no timeouts (we used 
the hard-coded value of '1' then)

what do you mean by 'timeouts'.

> Is there any other way I can improve the efficiency of it?

first.. I would examine the cpu utilization/throughput of your box.
maybe even reverting to 1.3.x/mod_gzip for a period and see if that 
works for you.

> Would changing DeflateBufferSize from 8096 to something else, help?
> Are there any plans to improve the efficiency of mod_deflate in the future?
not directly.. most of the time spent is in zlib's library, and the 
standard filter routines that apache uses.
> I'm running Apache/2.0.46 (prefork MPM) and mod_perl-1.99_09 on Red Hat 
> 9.  Server has dual 800Mhz CPUs and 1.5GB ram.

may I suggest you move to the worker MPM, I'm thinking you don't have 
enough ram in your machine for a pre-fork/mod-perl combo.
we run with 32 threads, and it seems ok most of the time.
just be careful of your 3rd party perl modules.. some may not be threadsafe.
( would be the appropiate place to ask about that)

> Thanks
> -bill


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