| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Jaime Casanova <jaime(dot)casanova(at)2ndquadrant(dot)com>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Patch: Write Amplification Reduction Method (WARM) |
| Date: | 2017-02-23 18:58:59 |
| Message-ID: | 20170223185859.fzop2i32ii5k7wk5@alvherre.pgsql |
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| Lists: | pgsql-hackers |
Bruce Momjian wrote:
> On Thu, Feb 23, 2017 at 03:45:24PM -0300, Alvaro Herrera wrote:
> > > and potentially trim the first HOT chain as those tuples become
> > > invisible.
> >
> > That can already happen even without WARM, no?
>
> Uh, the point is that with WARM those four early tuples can be removed
> via a prune, rather than requiring a VACUUM. Without WARM, the fourth
> tuple can't be removed until the index is cleared by VACUUM.
I *think* that the WARM-updated one cannot be pruned either, because
it's pointed to by at least one index (otherwise it'd have been a HOT
update). The ones prior to that can be removed either way.
I think the part you want (be able to prune the WARM updated tuple) is
part of what Pavan calls "turning the WARM chain into a HOT chain", so
not part of the initial patch. Pavan can explain this part better, and
also set me straight in case I'm wrong in the above :-)
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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