Re: [HACKERS] Vacuum: allow usage of more than 1GB of work mem

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/
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