| From: | Andrei Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> |
|---|---|
| To: | jian he <jian(dot)universality(at)gmail(dot)com> |
| Cc: | Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Richard Guo <guofenglinux(at)gmail(dot)com>, Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>, vignesh C <vignesh21(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Teodor Sigaev <teodor(at)sigaev(dot)ru>, David Rowley <dgrowleyml(at)gmail(dot)com>, "a(dot)rybakina" <a(dot)rybakina(at)postgrespro(dot)ru> |
| Subject: | Re: POC: GROUP BY optimization |
| Date: | 2024-05-21 09:01:19 |
| Message-ID: | 282f19f0-cbae-4233-9344-07307c044696@postgrespro.ru |
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| Lists: | pgsql-hackers |
On 20/5/2024 15:54, jian he wrote:
> As mentioned previously,
> both A and B can use Incremental Sort, set_cheapest will choose the A
> instead of B,
> because A step generated path **first** satisfies increment sort.
Yeah, I agree with your analysis.
Looking into the cost_incremental_sort, I see that we have ten
group_tuples. This value doesn't depend on how many presorted keys (1 or
2) we use. This is caused by default estimation.
Given the current circumstances, it seems unlikely that we can make any
significant changes without introducing a new sort cost model that
accounts for the number of sorted columns.
--
regards,
Andrei Lepikhov
Postgres Professional
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