Re: hashagg slowdown due to spill changes
От | Tomas Vondra |
---|---|
Тема | Re: hashagg slowdown due to spill changes |
Дата | |
Msg-id | 20200616165449.qkrxzhe2tdxnjaza@development обсуждение исходный текст |
Ответ на | Re: hashagg slowdown due to spill changes (Jeff Davis <pgsql@j-davis.com>) |
Список | pgsql-hackers |
On Mon, Jun 15, 2020 at 07:38:45PM -0700, Jeff Davis wrote: >On Mon, 2020-06-15 at 11:19 -0400, Robert Haas wrote: >> On Mon, Jun 15, 2020 at 9:34 AM Tomas Vondra >> <tomas.vondra@2ndquadrant.com> wrote: >> > But just reverting 4cad2534d will make this much worse, I think, as >> > illustrated by the benchmarks I did in [1]. >> >> I share this concern, although I do not know what we should do about >> it. > >I attached an updated version of Melanie's patch, combined with the >changes to copy only the necessary attributes to a new slot before >spilling. There are a couple changes: > >* I didn't see a reason to descend into a GroupingFunc node, so I >removed that. > >* I used a flag in the context rather than two separate callbacks to >the expression walker. > >This patch gives the space benefits that we see on master, without the >regression for small numbers of tuples. I saw a little bit of noise in >my test results, but I'm pretty sure it's a win all around. It could >use some review/cleanup though. > Looks reasonable. I can't redo my tests at the moment, the machine is busy with something else. I'll give it a try over the weekend. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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