| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Richard Guo <guofenglinux(at)gmail(dot)com> |
| Cc: | Justin Pryzby <pryzby(at)telsasoft(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Taylor Vesely <tvesely(at)pivotal(dot)io>, Adam Lee <ali(at)pivotal(dot)io>, Melanie Plageman <mplageman(at)pivotal(dot)io>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Memory-Bounded Hash Aggregation |
| Date: | 2020-03-28 19:29:29 |
| Message-ID: | 1dceb76c04e3b95268036f797f3dde7f8480a448.camel@j-davis.com |
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| Lists: | pgsql-hackers |
On Fri, 2020-03-27 at 02:31 +0100, Tomas Vondra wrote:
> On Thu, Mar 26, 2020 at 05:56:56PM +0800, Richard Guo wrote:
> > If nbatches is some number between 1.0 and 2.0, we would have a
> > negative
> > depth. As a result, we may have a negative cost for hash
> > aggregation
> > plan node, as described in [1].
> > numGroups / ngroups_limit );
>
> and we should probably do
>
> nbatches = ceil(nbatches);
>
Thank you both. I also protected against nbatches == 0 (shouldn't
happen), and against num_partitions <= 1. That allowed me to remove the
conditional and simplify a bit.
Regards,
Jeff Davis
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