Date: Sat, 31 May 2014 16:09:36 +0200
From: Andres Freund <andres@2ndquadrant.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Craig Ringer <craig@2ndquadrant.com>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: FOR [SHARE|UPDATE] NOWAIT may still block in
 EvalPlanQualFetch
Message-ID: <20140531140936.GC4286@awork2.anarazel.de>
References: <51FB6703.9090801@2ndquadrant.com>
 <20140131212808.GR19957@momjian.us>
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Hi,

On 2014-01-31 16:28:08 -0500, Bruce Momjian wrote:
> On Fri, Aug  2, 2013 at 04:00:03PM +0800, Craig Ringer wrote:
> > FOR SHARE|UPDATE NOWAIT will still block if they have to follow a ctid
> > chain because the call to EvalPlanQualFetch doesn't take a param for
> > noWait, so it doesn't know not to block if the updated row can't be locked.
> > 
> > The attached patch against master includes an isolationtester spec to
> > demonstrate this issue and a proposed fix. Builds with the fix applied
> > pass "make check" and isolationtester "make installcheck".
> > 
> > To reach this point you need to apply the patch in
> > http://www.postgresql.org/message-id/51FB4305.3070600@2ndquadrant.com
> > first, otherwise you'll get stuck there and won't touch the code changed
> > in this patch.
> 
> The above looks like a legitimate patch that was not applied:
> 
> 	http://www.postgresql.org/message-id/51FB6703.9090801@2ndquadrant.com
> 
> The patch mentioned in the text above was applied, I think.

Craig: I think you should add this to the next CF. Seems like something
we should fix, but which isn't super urgent. But when the skip locked
stuff comes in it'll be more relevant.
Might also need a rebase.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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