Skip site navigation (1) Skip section navigation (2)

Re: WAL logging of SELECT ... INTO command

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
Cc: Qingqing Zhou <zhouqq(at)cs(dot)toronto(dot)edu>, pgsql-performance(at)postgresql(dot)org
Subject: Re: WAL logging of SELECT ... INTO command
Date: 2006-03-24 13:47:20
Message-ID: 20060324134720.GA25359@surnet.cl (view raw or flat)
Thread:
Lists: pgsql-patchespgsql-performance
Jim C. Nasby wrote:
> On Fri, Mar 24, 2006 at 08:39:02AM -0400, Alvaro Herrera wrote:
> > Jim C. Nasby wrote:
> > 
> > > Why would the content of the old_table be unreliable? If we've replayed
> > > logs up to the point of the CTAS then any data that would be visible to
> > > the CTAS should be fine, no?
> > > 
> > > Though, the way Tom put it in one of his replies it sounds like WAL
> > > doesn't do any kind of statement logging, only data logging. If that's
> > > the case I'm not sure that the CTAS would actually get replayed. But I
> > > suspect I'm just misunderstanding...
> > 
> > The CTAS doesn't get logged (nor replayed obviously).  What happens is
> > that the involved files are fsync'ed before transaction commit, AFAIR.
> 
> Ahh, yes, that sounds right. Might be a nice gain to be had if there was
> some way to log the statement, but I suspect getting WAL to support that
> would be extremely non-trivial.

None at all, at least in the current incarnation, I think, because said
query execution is dependent on the contents of the FSM, which is itself
dependent on the timing of VACUUM and other stuff.  Such an action,
running with a different FSM content, can very trivially cause data
corruption.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

In response to

Responses

pgsql-performance by date

Next:From: Jim C. NasbyDate: 2006-03-24 13:59:46
Subject: Re: WAL logging of SELECT ... INTO command
Previous:From: Michael FuhrDate: 2006-03-24 13:32:53
Subject: Re: Array performance

pgsql-patches by date

Next:From: Jim C. NasbyDate: 2006-03-24 13:59:46
Subject: Re: WAL logging of SELECT ... INTO command
Previous:From: Jim C. NasbyDate: 2006-03-24 13:01:21
Subject: Re: WAL logging of SELECT ... INTO command

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group