Re: installcheck failing on psql_crosstab

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: installcheck failing on psql_crosstab
Date: 2016-06-06 15:28:37
Message-ID: 20160606152837.GA391408@alvherre.pgsql
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Tom Lane wrote:
> Alvaro Herrera <alvherre(at)2ndquadrant(dot)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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