Re: Plan stability versus near-exact ties in cost estimates

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Plan stability versus near-exact ties in cost estimates
Date: 2012-04-20 15:49:02
Message-ID: 8196.1334936942@sss.pgh.pa.us
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"Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at> writes:
> Tom Lane wrote:
>> Um, that is what the proposed patch does.

> I was referring to the first two lines that the patch removes.
> I guess I don't understand why they should go.

What we'd have left after the proposed removal is

if (new_path->rows < old_path->rows)
remove_old = true; /* new dominates old */
else
accept_new = false; /* old equals or dominates new */

There's no need to make more than one test on the rows values.

regards, tom lane

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