Re: Re: [COMMITTERS] pgsql: Implement multivariate n-distinct coefficients

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Re: [COMMITTERS] pgsql: Implement multivariate n-distinct coefficients
Date: 2017-03-24 19:21:18
Message-ID: 20170324192118.7cvlqhfx6p5ecdnd@alvherre.pgsql
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Tom Lane wrote:

> Why not use COSTS OFF? Or I'll put that even more strongly: all the
> existing regression tests use COSTS OFF, exactly to avoid this sort of
> machine-dependent output. There had better be a really damn good
> reason not to use it here.

If we use COSTS OFF, the test is completely pointless, as the plans look
identical regardless of whether the multivariate stats are being used or
not.

If we had a ROWS option to ANALYZE that showed estimated number of rows
but not the cost, that would be an option.

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

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