Re: Disk-based hash aggregate's cost model
От | Tomas Vondra |
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Тема | Re: Disk-based hash aggregate's cost model |
Дата | |
Msg-id | 20200904125640.wsk77dohvrdfu255@development обсуждение исходный текст |
Ответ на | Re: Disk-based hash aggregate's cost model (Jeff Davis <pgsql@j-davis.com>) |
Ответы |
Re: Disk-based hash aggregate's cost model
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Список | pgsql-hackers |
On Thu, Sep 03, 2020 at 05:53:43PM -0700, Jeff Davis wrote: >On Tue, 2020-09-01 at 23:19 +0200, Tomas Vondra wrote: >> FWIW any thoughts about the different in temp size compared to >> CP_SMALL_TLIST? > >Are you referring to results from a while ago? In this thread I don't >see what you're referring to. > >I tried in a simple case on REL_13_STABLE, with and without the >CP_SMALL_TLIST change, and I saw only a tiny difference. Do you have a >current case that shows a larger difference? > I'm referring to the last charts in the message from July 27, comparing behavior with CP_SMALL_TLIST fix vs. master (which reverted/replaced the CP_SMALL_TLIST bit). Those charts show that the CP_SMALL_TLIST resulted in smaller temp files (per EXPLAIN ANALYZE the difference is ~25%) and also lower query durations (also in the ~25% range). I can repeat those tests, if needed. [1] https://www.postgresql.org/message-id/20200724012248.y77rpqc73agrsvb3@development >The only thing I can think of that might change is the size of the null >bitmap or how fields are aligned. > Maybe. Not sure. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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