Re: IIS times out on large post requests

From: Rainer Sabelka <>
Date: Thu, 10 Jul 2008 11:32:30 +0200

On Thursday 10 July 2008 02:07:35 Willy Tarreau wrote: Hi Willy,
thanks for your answer!

> Well, good and bad news. In fact I could not reproduce it. My kernel
> (2.6.25) has a bug with TCP SACKs which cause it to stop retransmitting
> after a loss... pretty sad. That was the problem I encountered when
> unplugging the cable. Disabling TCP SACKs fixed it and now I cannot
> reproduce the problem anymore. However, some code chunks look tricky and
> need deeper auditing. Also, I found a related bug which *might* have caused
> your problem but since I cannot reproduce it here, I cannot swear it's
> responsible.
> So could you :
> - check your kernel version, and if it's >=2.6.25, disable tcp sack :
> # echo 0 >/proc/sys/net/ipv4/tcp_sack

My kernel is 2.6.24-19 (ubuntu 8.04 server edition). I have already disabled sack but that did not help (also disabling tcp_window_scaling didn't have an effect). I also disabled tcp_frto (to solve a problem with one user who always got timeouts when dowloading large documents)

> - apply the attached patch if the problem persists after the change
> above.

I've applied the patch but deployed it only on my test-system, but there I cannot reproduce the problem.
But I'll install the patched version on the production system in the evening - and we will see tomorrow if it solves the problem.

> - report your findings.

Yes, I'll do.

Thanks again,

PS: I'm not even sure if this problem is caused by haproxy at all - there are so many components in the chain, any of them could theoretically be the culprit:
internet explorer 6 -> iptables firewall -> apache 2.2.8 (with mod_ssl and mod_proxy) -> haproxy -> IIS 6
But haproxy is for me the most logical place to start debugging. Is there a possibility to log the actual size of the request body, so that I can compare it with the content length? Received on 2008/07/10 11:32

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