linux-kernel - Re: After many hours all outbound connections get stuck in SYN

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Date:	Tue, 18 Dec 2007 19:32:26 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	James Nichols <jamesnichols3@...il.com>
Cc:	Jan Engelhardt <jengelh@...putergmbh.de>,
	linux-kernel@...r.kernel.org
Subject: Re: After many hours all outbound connections get stuck in SYN_SENT

James Nichols a écrit :
>> Here is a purely hypothethical (and in practice unlikely) idea:
>> Java opens up too many sockets (more than you really request) and the
>> kernel, for whatever reason, does not deliver packets to programs
>> which have maxed out their fds. Well it would already help if the
>> java blob was split into multiple blobs (assuming the problem
>> persists), as the best testcase is the smallest possible one. So if
>> it is reproducable without the web blob, great step there.
>>
>>     
>
>
> Right, I don't disagree with you there.  FWIW, I can disable entire
> parts of the application and have already narrowed down reproduction
> of this issue to the 200 threads that make the webservice calls, so it
> doesn't have anything to do with any of the GUI or other background
> services that my application executes.
>
>
> You said:
>
>   
>> Well you could still blame Java. I am sure that if you program was C,
>> the problem could be narrowed down much easier.
>>     
>
> I'm curious to know how this problem would be easier to narrow down if
> it were written in C.
>   
Well... please dont start a flame war :(

Back to your SYN_SENT problem, I suppose the remote IP is known, so you 
probably could post here the result of a tcdpump ?

tcpdump -p -n -s 1600 host IP_of_problematic_peer -c 500

Most probably remote peer received too many attempts from you, and a 
anti DOS mechanism is droping all SYN packets.

Ah well... I remember now that you mentioned tcp_sack setting had an 
effect, so forget the "Most probably..." and give some tcpdump traces :)





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