Re: A couple questions about ordered-set aggregates
От | Tomas Vondra |
---|---|
Тема | Re: A couple questions about ordered-set aggregates |
Дата | |
Msg-id | 20201030234948.kawgciecx4hyyud4@development обсуждение исходный текст |
Ответ на | A couple questions about ordered-set aggregates (Chapman Flack <chap@anastigmatix.net>) |
Список | pgsql-hackers |
On Sun, Oct 25, 2020 at 09:32:22PM -0400, Chapman Flack wrote: >I find I am allowed to create an ordered-set aggregate with a non-empty >direct argument list and no finisher function. Am I right in thinking >that's kind of nonsensical, as nothing will ever look at the direct args? > >Also, the syntax summary shows PARALLEL = { SAFE | RESTRICTED | UNSAFE } >in the ordered-set syntax variant, since 9.6, though that variant >accepts no combine/serial/deserial functions, and there's also >a note saying "Partial (including parallel) aggregation is currently >not supported for ordered-set aggregates." > >Does PARALLEL = { SAFE | RESTRICTED | UNSAFE } on an ordered-set >aggregate affect anything? > I may be missing something, but I believe PARALLEL = SAFE simply means it can be executed in the parallel part of the plan. That does not require support for partial aggregation - we simply don't support passing partial results to the leader, hence combine/serial/deserial functions are not needed. Not sure about the direct arguments. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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