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Re: LWLock Queue Jumping

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: LWLock Queue Jumping
Date: 2009-08-30 12:22:41
Message-ID: 1251634961.4839.1532.camel@ebony.2ndQuadrant (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Sun, 2009-08-30 at 09:03 +0300, Heikki Linnakangas wrote:

> The Hot Standby thing has been discussed, but no-one has actually posted
> a patch which does the locking correctly, where the ProcArrayLock is
> held while the SnapshotData WAL record is inserted. So there is no
> evidence that it's actually a problem, we might be making a mountain out
> of a molehill. It will have practically no effect on throughput, given
> how seldom SnapshotData records are written (once per checkpoint), but
> if it causes a significant bump to response times, that might be a problem.
> This is a good idea to keep in mind, but right now it feels like a
> solution in search of a problem.

The most important thing is to get HS committed and to do that I think
it is important that I show you I am willing to respond to review
comments. So I will implement it the way you propose and defer any
further discussion about lock contention. The idea here is a simple fix
and very easy enough to return to later, if we need it.

 Simon Riggs 

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