On mån, 2010-11-22 at 11:58 +0900, Itagaki Takahiro wrote: > * Did you see any performance regression by collation? > I found a bug in lc_collate_is_c(); result >= 0 should be > checked before any other checks. SearchSysCache1() here > would be a performance regression.
That code turned out to be buggy anyway, because it was using the "result" cache variable independent of the collation parameter. I did some profiling with this now. The problem is that this function lc_collate_is_c() would need to cache the "C-ness" property for any number of collations. Depending on what call pattern you expect or want to optimize for, you might end up caching most of the pg_collation catalog, which is actually the mandate of SearchSysCache, but the profile shows that SearchSysCache takes a large chunk of the additional run time. If I remove that branch altogether, that is, don't treat the C locale specially at all in the nondefault collation case, then using non-C locales as nondefault collation is almost as fast as using non-C locales as default location. However, using the C locale as a nondefault collation would then be quite slow (still faster that non-C locales). The solution would perhaps be a custom, lightweight caching system, but I haven't thought of one yet. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
