Re: installcheck failing on psql_crosstab - Mailing list pgsql-hackers

From Alvaro Herrera
Subject Re: installcheck failing on psql_crosstab
Date
Msg-id 20160606152837.GA391408@alvherre.pgsql
Whole thread Raw
In response to Re: installcheck failing on psql_crosstab  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: installcheck failing on psql_crosstab  (Michael Paquier <michael.paquier@gmail.com>)
List pgsql-hackers
Tom Lane wrote:
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:

> > I can't imagine that the server is avoiding hash aggregation on a 1MB
> > work_mem limit for data that's a few dozen of bytes.  Is it really doing
> > that?
> 
> Yup:

Aha.  Thanks for testing.

> Now that you mention it, this does seem a bit odd, although I remember
> that there's a pretty substantial fudge factor in there when we have
> no statistics (which we don't in this example).  If I ANALYZE ctv_data
> then it sticks to the hashagg plan all the way down to 64kB work_mem.

Hmm, so we could solve the complaint by adding an ANALYZE.  I'm open to
that; other opinions?

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services



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