Re: Inlining comparators as a performance optimisation

On 7 December 2011 15:15, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Dec 7, 2011 at 10:09 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> But it would still have to be prepared for detoasting,
>> so in the end I was unenthused.  Anyone who feels like testing could try
>> to prove me wrong about it though.
>
> I think that'd definitely be worth investigating (although I'm not
> sure I have the time to do it myself any time real soon).

I'll at least take a look at it. Sorting text is a fairly common case.
I'm not hugely enthused about spending too much time on work that will
only be useful if collate_is_c.

>> I don't believe that #2 blocks progress on #3
>> anyway.  I think #3 is in Peter's court, or yours if you want to do it.
>>
>> (BTW, I agree with your comments yesterday about trying to break down
>> the different aspects of what Peter did, and put as many of them as we
>> can into the non-inlined code paths.)

I'm confident that we should have everything for the simple case of
ordering by a single int4 and int8 column, and I think you'd probably
agree with that - they're extremely common cases. Anything beyond that
will need to be justified, probably in part by running additional
benchmarks.

> Cool.  Peter, can you rebase your patch and integrate it into the
> sortsupport framework that's now committed?

Yes, I'd be happy to, though I don't think I'm going to be getting
around to it this side of Friday. Since it isn't a blocker, I assume
that's okay.

The rebased revision will come complete with a well thought-out
rationale for my use of inlining specialisations, that takes account
of the trade-off against binary bloat that Tom highlighted. I wasn't
ignoring that issue, but I did fail to articulate my thoughts there,
mostly because I felt the need to do some additional research to
justify my position.

--
Peter Geoghegan       http://www.2ndQuadrant.com/
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