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

On Tue, Sep 16, 2014 at 1:45 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> Even though our testing seems to indicate that the memcmp() is
> basically free, I think it would be good to make the effort to avoid
> doing memcmp() and then strcoll() and then strncmp(). Seems like it
> shouldn't be too hard.

Really? The tie-breaker for the benefit of locales like hu_HU uses
strcmp(), not memcmp(). It operates on the now-terminated copies of
strings. There is no reason to think that the strings must be the same
size for that strcmp(). I'd rather only do the new opportunistic
"memcmp() == 0" thing when len1 == len2. And I wouldn't like to have
to also figure out that it's safe to use the earlier result, because
as it happens len1 == len2, or any other such trickery.

The bug fix that added the strcmp() tie-breaker was committed in 2005.
PostgreSQL had locale support for something like 8 years prior, and it
took that long for us to notice the problem. I would suggest that
makes the case for doing anything else pretty marginal. In the bug
report at the time, len1 != len2 anyway.

--
Peter Geoghegan