gzip - unexplained side effects
igor at sysoev.ru
Wed Nov 9 12:41:33 UTC 2011
On Tue, Nov 08, 2011 at 09:14:04PM -0500, dbanks wrote:
> I'm running nginx 1.0.0 in front of a FCGI backend. We've been running
> in production for about 4 months, and have really been impressed with
> the performance and stability of nginx.
> We run a medium-volume appliction: 1000 to 4000 requests/sec spread over
> 2 instances by an upstream round robin load balancer. We use
> keepalives, but keep them rather short given the request volume to keep
> the number of open connections manageable.
> Recently, I was working to improve our gzip settings. The largest
> change was that I added an explicit gzip buffer line (find my config
> below - the three lines that are commented out seem to be correlated
> with this issue)
> After the change, the volume of outbound traffic decreased measurably,
> as if gzip was not originally doing much due to inadequate buffer space.
> Great news!, or so I thought. What also changed was that the number of
> active connections fell by about 75% - the gzip change was somehow
> causing keepalives to be closed prematurely. Also, our volume of
> incoming requests decreased a bit: as if some requests were being
> aborted (though accepts == handled). The request volume makes
> debugging this particular issue somewhat troublesome, since I have yet
> to replicate it in a quiet instance.
> The guts of my configuration appear below. This is such an unexpected
> issue that I'm not doing a great job of setting up my question well.
> What I think I'd like to know is how could a change to the gzip buffers
> (or the other two commented changes) impact keepalives or overall
> connection negotiation? Also, any suggestions as to how to go about
> debugging it?
> sendfile off;
> tcp_nodelay on;
> ignore_invalid_headers on;
> if_modified_since off;
> gzip on;
> gzip_comp_level 9;
> gzip_disable "MSIE [1-6]\.(?!.*SV1)"
> #gzip_buffers 512 4k;
> #gzip_min_length 1100; #if it fits in one packet, no worries
> #gzip_http_version 1.1;
> keepalive_timeout 6;
> keepalive_requests 4;
If you comment gzip_buffers, you see the previous site state ?
What is typical uncompressed and compressed response size ?
The default gzip_buffers are "32 4k", so they can keep up to 128K.
And as it was already suggested it's better to use default
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