Subject: Re: Some queries starting to hang
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: "Craig A. James" <cjames@modgraph-usa.com>
Cc: pgsql-performance@postgresql.org
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Date: Tue, 06 Jun 2006 12:54:27 -0500

On Tue, 2006-06-06 at 12:50, Craig A. James wrote:
> Tom Lane wrote:
> >>The idea I just had was: why do we need EXPLAIN ANALYZE to run to
> >>completion? In severe cases like this thread, we might be able to
> >>discover the root cause by a *partial* execution of the plan, as long as
> >>it was properly instrumented. That way, the OP might have been able to
> >>discover the root cause himself...
> > 
> > 
> > I don't think that helps, as it just replaces one uncertainty by
> > another: how far did the EXPLAIN really get towards completion of the
> > plan?  You still don't have any hard data.
> 
> But at least you have some data, which is better than no data.  Even knowing that the plan got stuck on a particular node of the query plan could be vital information.  For a query that never finishes, you can't even find out where it's getting stuck.
> 
> That's why Simon's proposal might help in some particularly difficult situations.

Hmmmmm.  I wonder if it be hard to have explain analyze have a timeout
per node qualifier?  Something that said if it takes more than x
milliseconds for a node to kill the explain analyze and list the up to
the nasty node that's using all the time up?

That would be extremely useful.