Re: Additional size of hash table is alway zero for hash aggregates

From: Andres Freund <andres(at)anarazel(dot)de>
To: Pengzhou Tang <ptang(at)pivotal(dot)io>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Jeff Davis <pgsql(at)j-davis(dot)com>
Subject: Re: Additional size of hash table is alway zero for hash aggregates
Date: 2020-03-12 19:16:26
Message-ID: 20200312191626.cd3i7iqawz4bcphm@alap3.anarazel.de
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Hi,

On 2020-03-12 16:35:15 +0800, Pengzhou Tang wrote:
> When reading the grouping sets codes, I find that the additional size of
> the hash table for hash aggregates is always zero, this seems to be
> incorrect to me, attached a patch to fix it, please help to check.

Indeed, that's incorrect. Causes the number of buckets for the hashtable
to be set higher - the size is just used for that. I'm a bit wary of
changing this in the stable branches - could cause performance changes?

Greetings,

Andres Freund

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