Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)

On 2017-03-21 08:04:11 -0400, Robert Haas wrote:
> On Tue, Mar 21, 2017 at 6:56 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> >> Hmm, that test case isn't all that synthetic.  It's just a single
> >> column bulk update, which isn't anything all that crazy, and 5-10%
> >> isn't nothing.
> >>
> >> I'm kinda surprised it made that much difference, though.
> >>
> >
> > I think it is because heap_getattr() is not that cheap.  We have
> > noticed the similar problem during development of scan key push down
> > work [1].
> 
> Yeah.  So what's the deal with this?  Is somebody working on figuring
> out a different approach that would reduce this overhead?

I think one reasonable thing would be to use slots here, and use
slot_getsomeattrs(), with a pre-computed offset, for doing the
deforming.  Given that more than one place run into the issue with
deforming cost via heap_*, that seems like something we're going to have
to do.  Additionally the patches I had for JITed deforming all
integrated at the slot layer, so it'd be a good thing from that angle as
well.

Deforming all columns at once would also a boon for the accompanying
index_getattr calls.


Greetings,

Andres Freund