Re: limit clause breaks query planner?

"Matt Smiley" <mss@rentrak.com> writes:
>  So an Index Scan is always going to have a higher cost estimate than
>  an equivalent Seq Scan returning the same result rows (unless
>  random_page_cost is < 1).  That's why I think the planner is always
>  preferring the plan that uses a Seq Scan.

If that were the case, we'd never choose an indexscan at all...

It's true that a plain indexscan is not preferred for queries that will
return a large fraction of the table.  However, it should be willing to
use a bitmap scan for this query, given default cost settings (the
default cost settings will cause it to prefer bitmap scan for retrieving
up to about a third of the table, in my experience).  I too am confused
about why it doesn't prefer that choice in the OP's example.  It would
be interesting to alter the random_page_cost setting and see if he gets
different results.

            regards, tom lane