| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Block level parallel vacuum WIP |
| Date: | 2017-01-10 16:23:10 |
| Message-ID: | CAGTBQpZt9AWDwhDunLkkCG_WTNxYmv-007ePUAhn7+piCDYdYA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jan 10, 2017 at 6:42 AM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>> Does this work negate the other work to allow VACUUM to use >
>> 1GB memory?
>
> Partly yes. Because memory space for dead TIDs needs to be allocated
> in DSM before vacuum worker launches, parallel lazy vacuum cannot use
> such a variable amount of memory as that work does. But in
> non-parallel lazy vacuum, that work would be effective. We might be
> able to do similar thing using DSA but I'm not sure that is better.
I think it would work well with DSA as well.
Just instead of having a single segment list, you'd have one per worker.
Since workers work on disjoint tid sets, that shouldn't pose a problem.
The segment list can be joined together later rather efficiently
(simple logical joining of the segment pointer arrays) for the index
scan phases.
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