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Re: Information about WAL Configuration needs an update

From: Rafael Martinez <r(dot)m(dot)guerrero(at)usit(dot)uio(dot)no>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: pgsql-docs(at)postgresql(dot)org
Subject: Re: Information about WAL Configuration needs an update
Date: 2011-06-13 18:25:11
Message-ID: 1307989511.2862.810.camel@core2 (view raw, whole thread or download thread mbox)
Lists: pgsql-docs
On Mon, 2011-06-13 at 13:24 -0400, Robert Haas wrote:
> On Fri, Jun 3, 2011 at 3:42 AM, Rafael Martinez
> >
> > You can see the graph with the generation of WAL files + some extra
> > information for this test here:
> >
> > What do you think? Shouldn't we update the documentation with some
> > information about this?
> Perhaps, but we'd have to think of something intelligent to say about
> it first.  We can't remove the old WAL files until we successfully
> checkpoint, and so I think if checkpoints are taking a very long to
> complete or failing altogether, there's actually no upper bound.  I
> don't think we have any kind of "hard stop" where, if no log space is
> available, we just refuse to process write transactions - such a thing
> would seem to be rather dangerous.

Well, a good start will be to try to identify or describe the situations
where checkpoints can take very long to complete or fail altogether.

I have the first one: Creating a large GIN index on a tsvector column. I
don't know why, maybe somebody who knows postgres internals can explain
why a creation of an index can create this situation.

Rafael Martinez Guerrero
Center for Information Technology
University of Oslo, Norway

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