This thread: http://www.varnish-cache.org/lists/pipermail/varnish-misc/2010-December/005258.html
- Stig On Wed, Jan 5, 2011 at 11:44 PM, George Georgovassilis < [email protected]> wrote: > Hello Stig, > > Thanks for the insight. I'm still on the logs, though not sure where to > start - it's not like that there are any errors in it so I'm not really sure > what to look for. Do you have a pointer to that discussion you are referring > to? > > > On 05.01.2011 23:41, Stig Bakken wrote: > > This seems similar to what I've been seeing, described in an earlier thread > from before christmas. In my case it was not during benchmarking, but when > serving production load of around 300 req/s per server. Modern tcpip stacks > on modern hardware should handle this without blinking. > > Did you have the chance to capture the problem with varnishlog so you can > replay/analyze it? > > - Stig > > On Wed, Jan 5, 2011 at 11:18 PM, George Georgovassilis < > [email protected]> wrote: > >> I removed the varnish instance so that the load generator is directly >> hitting Tomcat. Naturally, the request rate drops to 70 requests/sec with a >> CPU load of 100%... however connections don't drop anymore, no timeouts >> occur and the application remains pretty responsive. To recap, these are the >> possible scenarios: >> >> 1. The networking layer is overtaxed with the original 300 reqs/sec. I >> don't believe that, because the load generator doesn't record any dropped >> connections while a simple browser can't connect. >> >> 2. Tomcat is overtaxed. That also seems not plausible, since it is not >> servicing any requests under the load test - all is done by varnish. Even >> if, as I said when removing varnish from in between, it serves the requests >> just fine. >> >> 3. Varnish is overtaxed. Somehow that also doesn't make sense, since it is >> servicing the load generator just fine... but will refuse to serve browser >> requests. >> >> 4. Varnish, when under load, is picky about what connections to serve. >> >> I'm stuck :-) >> >> >> On 05.01.2011 17:59, Bob Camp wrote: >> >>> Hi >>> >>> Running simple load tests both on Apache directly, and on Varnish - both >>> seem to experience "long delays" on a small percentage of the requests. >>> The >>> problem does not appear to happen with low loads. It does come up as CPU >>> usage becomes an issue. It also is hard to make happen with a single >>> stream >>> of requests. It seems to come up much quicker with many requests done in >>> parallel. >>> >>> I've always *assumed* that the poor little TCP/IP hamster simply ran out >>> of >>> breath and started dropping connections. >>> >>> Bob >>> >>> -----Original Message----- >>> From: [email protected] >>> [mailto:[email protected]] On Behalf Of George >>> Georgovassilis >>> Sent: Wednesday, January 05, 2011 11:18 AM >>> To: [email protected] >>> Subject: Re: Connections dropped under load >>> >>> Hello Cosimo, >>> >>> Thank you for the quick reply. After your hint I had the tests run again >>> but couldn't detect that pattern. What susprised me though after looking >>> through the logs is that almost all requests by the load generator >>> complete in a timely manner (< 1 sec), but all requests generated by a >>> real browser (IE, FF, Opera) will be served much later or even run into >>> a timeout. >>> >>> On 05.01.2011 16:30, Cosimo Streppone wrote: >>> >>>> On Wed, 05 Jan 2011 16:20:31 +0100, George Georgovassilis >>>> <[email protected]> wrote: >>>> >>>> I'm having trouble with dropped connections under a loadtest. >>>>> >>>>> The problem: As a measure for response, I am requesting an image from >>>>> the webapp running in Tomcat while the loadtest is underway. However >>>>> that either times out or is delivered after several seconds. Varnishlog >>>>> will often either not show the request (RxURL) at all, or show it >>>>> several seconds after the browser dispatched it. >>>>> >>>> Hi George, >>>> >>>> if you measure the time you mention as "several seconds" >>>> and it's either 3 or 9 seconds, I think what you're seeing >>>> is a client-side TCP retransmit timeout. >>>> >>>> I experienced that, both under load testing, >>>> and in real production setups. >>>> >>>> >>> _______________________________________________ >>> varnish-misc mailing list >>> [email protected] >>> http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc >>> >>> >> >> _______________________________________________ >> varnish-misc mailing list >> [email protected] >> http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc >> > > > > -- > Stig Bakken > CTO, Zedge.net - free your phone! > > > > _______________________________________________ > varnish-misc mailing list > [email protected] > http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc > -- Stig Bakken CTO, Zedge.net - free your phone!
_______________________________________________ varnish-misc mailing list [email protected] http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc
