On Wed, 13 Mar 2002, Nick Fankhauser wrote:
> So my question in general is why does PGSQL opt to use the index when
> looking for the single field row, and not use it when looking for the other
> 23768 rows?
Because in many cases the sequence scan will be faster than an index scan
when you're trying to get most of the rows of the table. Since the tuple
validity is in the table row and not the index, it's still got to check
the table which would involve lots of random reads into that file, so
you're doing even more disk operations and less efficient ones.
