| From: | Corey Huinker <corey(dot)huinker(at)gmail(dot)com> |
|---|---|
| To: | James Coleman <jtc331(at)gmail(dot)com> |
| Cc: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Maxim Ivanov <hi(at)yamlcoder(dot)me>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: optimisation? collation "C" sorting for GroupAggregate for all deterministic collations |
| Date: | 2020-03-23 01:00:41 |
| Message-ID: | CADkLM=dhELi6fK8jbPVzfwwnzO729zDzTt=mVax9tJybr0=3_Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
>
> Perhaps this is what you mean by "deterministic", but isn't it
> possible for some collations to treat multiple byte sequences as equal
> values? And those multiple byte sequences wouldn't necessarily occur
> sequentially in C collation, so it wouldn't be possible to work around
> that by having the grouping node use one collation but the sorting
> node use the C one.
>
> If my memory is incorrect, then this sounds like an intriguing idea.
>
>
I could see the value in a hash aggregate on C-collation that then passes
itself as a partial aggregate up to another step which applies the
collation and then finalizes the aggregation before sorting
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