27 липня 2009 р. 17:18 Tom Lane <t...@sss.pgh.pa.us> написав:
> =?KOI8-U?B?96bUwcymyiD0yc3eydvJzg==?= <tiv...@gmail.com> writes: > > Actually what I am talking about is to make OR with UNION (or UNION-like > > because it's a little different depending on input rows uniqueness) as an > > option. All of OR parts can use/not use different strategies (including > > multiple different idexes or hash joins). > > AFAICS you're proposing re-inventing the old implementation of OR'd > indexscans. We took that out when we added bitmap scans because it > didn't have any performance advantage over BitmapOr. > It's not tied to indexscans at all. Different parts can do (as in UNION) totally different strategy - e.g. perform two hash joins or perform merge join for one part and nested loop for another or ... As of performance - see above in this thread. UNION now often provides much better performance when different parts of OR expression involve different additional tables.
