Re: AW: like and optimization

Tom Lane writes:

> Zeugswetter Andreas SB <ZeugswetterA(at)wien(dot)spardat(dot)at> writes:
> > Just to understand things correctly. Is the Like optimization disabled
> > for all non-ASCII char sets, or (imho correctly) for non charset ordered
> > collations (LC_COLLATE) ?
>
> Currently it's disabled whenever LC_COLLATE is neither C nor POSIX.
> We can add other names to the "OK" list as we verify that they are safe
> (see locale_is_like_safe() in src/backend/utils/adt/selfuncs.c).

I have pretty severe doubts that any locale for a language that uses the
Latin, Cyrillic, or Greek alphabets (i.e., those that are conceptually
similar to English) is like-optimization safe (for the optimization
algorithm in its current state), at least across all platforms.
Somewhere a vendor is going to adhere to some ISO standard and implement
the same multi-pass "letters first" rules that we observed in en_US.

There should be some extensive "stress test" that a locale should have to
pass before being labelled safe.

--
Peter Eisentraut peter_e(at)gmx(dot)net http://yi.org/peter-e/