On 20/04/14 12:08, Thomas Kellerer wrote: >> Example: >> >> btree (fmb_id, action_type) >> btree (fmb_id) >> [...] > > Btw: in the above example the second one is definitely not needed. > Any query that uses the second one (single column) can also use the > first one. I know. But the single column index is 3534 MB the 2-column one 4963 MB. The number of rows per distinct fmb_id is very small, usually 1 or 2. So, if a query looks for "fmb_id=A and action_type=B", it has to filter out only one row if the first index is not available. Hence, I thought maybe the lower size of the index and the higher compactness per page could outweigh the more direct access provided by the 2-column index. I am quite sure there is no query that qualifies for an index-only scan on the 2-column index. Torsten -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
