| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Vacuum: allow usage of more than 1GB of work mem |
| Date: | 2017-01-20 21:34:14 |
| Message-ID: | 20170120213414.lyfmiawnrkxhs32k@alvherre.pgsql |
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| Lists: | pgsql-hackers |
Alvaro Herrera wrote:
> There was no discussion whatsoever of the "prefetch" patch in this
> thread; and as far as I can see, nobody even mentioned such an idea in
> the thread. This prefetch patch appeared out of the blue and there was
> no discussion about it that I can see. Now I was about to push it after
> some minor tweaks, and went to search where was its justification, only
> to see that there was none. Did anybody run tests with this patch?
>
> I attach it now one more time. My version is based on the latest
> Claudio posted at
> https://postgr.es/m/CAGTBQpa464RugxYwxLTtDi=Syv9GnGFcJK8uZb2fR6NDDqULaw@mail.gmail.com
> I don't know if there are differences to the version first posted.
> I only changed the magic number 32 to a #define, and added a
> CHECK_FOR_INTERRUPTS in the prefetching loop.
Ah, I found the justification here:
https://www.postgresql.org/message-id/flat/CAGTBQpa464RugxYwxLTtDi%3DSyv9GnGFcJK8uZb2fR6NDDqULaw%40mail.gmail.com#CAGTBQpbayY-t5-ySW19yQs1dBqvV6dm8dmdpTv_FWXmDC0A0cQ%40mail.gmail.com
apparently the truncate scan is 4x-6x faster with this prefetching.
Nice!
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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