On 04/08/2014 08:02 PM, Peter Geoghegan wrote:
> On Tue, Apr 8, 2014 at 3:12 AM, Heikki Linnakangas
> <hlinnakangas@vmware.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.
Sure, submit the second as a cumulative patch.
> By far the largest improvements come
> from 2), while 1) doesn't regress anything.
Right. But 1) is the baseline we need to evaluate 2) against.
- Heikki