On Tue, Apr 11, 2023 at 06:09:41PM -0700, Ajay P S wrote: > I am trying to understand the Plan tree for select queries. Can you > please help me with the below queries? > > 1) Why is there a difference in plan tree for these two queries? User > table tidx1 has an index on column 'a' .
Based on the query planner's cost estimate of the different scans. > 2) Why do we do Index scan and not Bitmap Index Scan for catalog tables? There's no reason why it can't happen in general. But you queried pg_class on a unique column, returning at most one row. A bitmap couldn't help by making the I/O more sequential. It can only add overhead. You can compare the costs of various plans by running EXPLAIN with various enable_* GUCs to off. BTW, your question should be directed to another list - this list is for bug reports and development. -- Justin
