Mike Winter <mike.winter@*nospam**frontlogic.com> writes:
> My query is of the form:
> SELECT col, count(col) FROM tab WHERE id IN (3,
> 4,7,2, ...) GROUP BY COL ORDER BY count
> for a very large number of rows.
> I have an index on id, so the explain looks like:
> Aggregate (cost=12.12..12.14 rows=1 width=5)
> -> Group (cost=12.12..12.13 rows=4 width=5)
> -> Sort (cost=12.12..12.12 rows=4 width=5)
> -> Index Scan using col_id_idx2, col_id_idx2, col_id_idx2,
> col_id_idx2 on tab (cost=0.00..12.08 rows=4 width=5)
The planner obviously does not think this is a large table (the cost
estimates correspond to very small numbers of pages). I wonder
whether you have ever VACUUMed or ANALYZEd the table.
regards, tom lane