Rajesh Kumar Mallah <mallah.rajesh@xxxxxxxxx> wrote: > just by removing the order by co_name reduces the query time > dramatically from ~ 9 sec to 63 ms. Can anyone please help. The reason is that one query allows it to return *any* 25 rows, while the other query requires it to find a *specific* set of 25 rows. It happens to be faster to just grab any old set of rows than to find particular ones. If the actual results you need are the ones sorted by name, then forget the other query and focus on how you can retrieve the desired results more quickly. One valuable piece of information would be to know how many rows the query would return without the limit. It's also possible that your costing factors may need adjustment. Or you may need to get finer-grained statistics -- the optimizer thought it would save time to use an index in the sequence you wanted, but it had to scan through 2212 rows to find 25 rows which matched the selection criteria. It might well have been faster to use a table scan and sort than to follow the index like that. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
