Re: Patch: Write Amplification Reduction Method (WARM)

Robert Haas wrote:
> On Wed, Mar 8, 2017 at 2:30 PM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
> > Not really -- it's a bit slower actually in a synthetic case measuring
> > exactly the slowed-down case. See
> > https://www.postgresql.org/message-id/CAD__OugK12ZqMWWjZiM-YyuD1y8JmMy6x9YEctNiF3rPp6hy0g@mail.gmail.com
> > I bet in normal cases it's unnoticeable. If WARM flies, then it's going
> > to provide a larger improvement than is lost to this.
>
> Hmm, that test case isn't all that synthetic. It's just a single
> column bulk update, which isn't anything all that crazy,

The problem is that the update touches the second indexed column. With
the original code we would have stopped checking at that point, but with
the patched code we continue to verify all the other indexed columns for
changes.

Maybe we need more than one bitmapset to be given -- multiple ones for
for "any of these" checks (such as HOT, KEY and Identity) which can be
stopped as soon as one is found, and one for "all of these" (for WARM,
indirect indexes) which needs to be checked to completion.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services