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Re: CentOS & PostgreSQL help re: TIME_WAIT

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: Reggie Euser <reggie(at)busicast(dot)com>, pgsql-admin(at)postgresql(dot)org
Subject: Re: CentOS & PostgreSQL help re: TIME_WAIT
Date: 2010-01-29 19:26:10
Message-ID: 8848.1264793170@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-admin
Greg Stark <gsstark(at)mit(dot)edu> writes:
> On Thu, Jan 28, 2010 at 8:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> In general, sockets sitting a long time in TIME_WAIT would be a network
>> problem. That state means the user process already closed the socket
>> and the network stack is waiting for the other end to acknowledge
>> connection closure.

> I think you're describing FIN_WAIT. TIME_WAIT is after the finack has
> been sent and the connection is well and truly dead. The same
> host/port pair can't be reused for 2*msl in case the finack needs to
> be resent or a duplicate fin arrives.

> Normally the server uses SO_LINGER and skips TIME_WAIT so it can
> listen on the same port immediately and accept more connections.  So
> only the client enters TIME_WAIT and its for some random high-numbered
> port that the OS won't hand out until it expires.

Hmm.  This may well be a platform-specific behavior of the network
stack.  On my mail machine (running a pretty ancient HPUX release)
I can normally see a dozen or so inbound connections to port 25
that are sitting in TIME_WAIT state, probably reflecting spambots
that didn't bother to close the connection gracefully.  It's possible
that a newer network stack would bypass that state.  But in any case
the userland process has definitely dropped the connection, right?
So it's not Postgres' issue, it's a networking issue.

			regards, tom lane

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Subject: Re: CentOS & PostgreSQL help re: TIME_WAIT
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