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From "Craig A. James" <cja...@emolecules.com>
Subject Re: [users@httpd] Some VirtualHosts extremely slow, others very fast
Date Thu, 09 Dec 2010 19:36:23 GMT
I have found the trigger for my horrible performance problem, but it is surprising.

Apache gets slow when there are too many "Allow from" directives, in this case, about 105
"Allow from" specs that are a mix of single IP addresses, partial IP address and netmasks:

   11.12.13.14
   21.22.
   21.123.0.0/16

... and so forth.  Note that there are *no* hostnames, just IP addresses and netmasks so it's
not a DNS lookup problem.

This is very consistent.  If we take out the "Allow from", Apache works.  If we add them back,
the web site gets extremely slow.  But not for all users.  Only some customers see this problem;
most have excellent performance all the time.

When we run wireshark to analyze TCP/IP traffic with all 105 "Allow from" in place, it starts
dropping TCP/IP ACK packets and having to resend a lot of data.  When we take the "Allow from"
out, the TCP/IP communication is smooth and fast.

Has anyone else run into this, and if so, how do you fix it?

This is on Apache 2.2.14 on Ubuntu 10.04.

Thanks,
Craig

>> On Dec 9, 2010 1:24 PM, "Craig A. James" <cjames@emolecules.com <mailto:cjames@emolecules.com>>
wrote:
>>
>> We operate one public web site and about 20 private web sites.  They're all the same
server, running the same Apache server instance (2.2.14-5ubuntu8.3).
>>
>> Most customers get excellent performance, but two customers get terrible response
times, but only on *some* of the VirtualHosts.  They get excellent responses from our public
site, but the very same page served from a private site can take over a minute to load.
>>
>> The VirtualHosts are configured identically except for the "Allow from" and "ServerName"
directives.  As far as I can tell, everything else is identical (except the specific database
it uses, but for these tests we're only loading static HTML pages).
>>
>> It appears that "www.ourdomain.com <http://www.ourdomain.com>" VirtualHosts
always work, but "xyz.ourdomain.com <http://xyz.ourdomain.com>" VirtualHosts give problems.
>>
>> Examining TCP/IP traffic using WireShark, it looks like the slow virtual hosts are
dropping ACK packets.  Each TCP/IP conversation starts out fast, but then there's a 5-second
gap in the middle of every HTTP response.  Yet if the very same user accesses a different
VirtualHost, there is no problem at all.
>>
>> We've been trying to figure this out for weeks with no luck.  Any ideas would be
greatly appreciated.
>>
>> Craig
>>
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