Re: Some mystery with execution plans on postgres 8.1

Boguk Maxim <astar@rambler-co.ru> writes:
> If short: adding index to table change execution plans on query which dont
> use new index.

After some experimentation I was able to create a similar misbehavior
here.  I think what is happening is that the added index is capturing
the bitmap scan plan, even though it ends up making that plan more
expensive and thus a loser to the plain indexscan.  The reason is this
bug:
http://archives.postgresql.org/pgsql-committers/2006-06/msg00064.php
which makes choose_bitmap_and sort the available indexes in the wrong
order.

            regards, tom lane