Bruce Momjian <pgman@candle.pha.pa.us> writes:
> However, assume tab2.col2 equals 3. I assume this would cause an index
> scan because the executor doesn't know about the most common value,
> right? Is it worth trying to improve that?
Oh, I see: you are assuming that a nestloop join is being done, and
wondering if it's worthwhile to switch dynamically between seqscan
and indexscan for each scan of the inner relation, depending on exactly
what value is being supplied from the outer relation for that scan.
Hmm.
Not sure if it's worth the trouble or not. Nestloop is usually a
last-resort join strategy anyway, and is unlikely to be picked when the
tables are large enough to make performance be a big issue.
regards, tom lane