Re: Information about WAL Configuration needs an update

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: http://folk.uio.no/rafael/total_wal/
> >
> > 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.

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

PGP Public Key: http://folk.uio.no/rafael/