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

From: "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at>
To: "Tom Lane *EXTERN*" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Plan stability versus near-exact ties in cost estimates
Date: 2012-04-21 08:33:43
Message-ID: D960CB61B694CF459DCFB4B0128514C2049FCE82@exadv11.host.magwien.gv.at (view raw or flat)
Thread:
Lists: pgsql-hackers
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.

I see, thanks for explaining.

Yours,
Laurenz Albe

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