Re: B-Tree support function number 3 (strxfrm() optimization)

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On Tue, Apr 8, 2014 at 3:12 AM, Heikki Linnakangas
<hlinnakangas(at)vmware(dot)com> wrote:
> 1. Avoid fmgr and shim overhead
> 2. Use strxfrm to produce a pseudo-leading key that's cheaper to compare.
>
> In that case, these changes need to be analyzed separately. You don't get to
> "make up" for the losses by the second part by the gains from the first
> part. We could commit just the first part (for 9.5!), and that has to be the
> baseline for the second part.

Yes, that's right. Robert already submitted a patch that only did 1)
almost 2 years ago. That should have been committed at the time, but
wasn't. At the time, the improvement was put at about 7% by Robert. It
would be odd to submit the same patch that Robert withdrew already.

Why shouldn't 2) be credited with the same benefits as 1) ? It's not
as if the fact that the strxfrm() trick uses SortSupport is a
contrivance. I cannot reasonably submit the two separately, unless the
second in a cumulative patch. By far the largest improvements come
from 2), while 1) doesn't regress anything.

--
Peter Geoghegan