| From: | Teodor Sigaev <teodor(at)sigaev(dot)ru> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> |
| Cc: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Darafei Komяpa Praliaskouski <me(at)komzpa(dot)net>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Antonin Houska <ah(at)cybertec(dot)at>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] [PATCH] Incremental sort |
| Date: | 2018-04-07 16:18:00 |
| Message-ID: | 41aa271c-f97c-2d13-1b1a-c580b5e3a99d@sigaev.ru |
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| Lists: | pgsql-hackers |
> I dunno, how would you estimate whether this is actually a win or not?
> I don't think our model of sort costs is anywhere near refined enough
> or accurate enough to reliably predict whether this is better than
> just doing it in one step. Even if the cost model is good, it's not
> going to be better than our statistics about the number/size of the
> groups in the first column(s), and that's a notoriously unreliable stat.
I think that improvement in cost calculation of sort should be a
separate patch, not directly connected to this one. Postpone patches
till other part will be ready to get max improvement for postponed ones
doesn't seem to me very good, especially if it suggests some improvement
right now.
--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/
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