On Wed, Aug 7, 2013 at 3:34 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Claudio Freire <klaussfre...@gmail.com> writes: >> On Wed, Aug 7, 2013 at 3:12 PM, Robert DiFalco <robert.difa...@gmail.com> >> wrote: >>> I want to get the last call_activity record for a single user. > >> Create an index over (user_id, called desc), and do >> select * from call_activity where user_id = blarg order by called desc limit >> 1 > > Note that there's no particular need to specify "desc" in the index > definition. This same index can support searches in either direction > on the "called" column.
Yeah, but it's faster if it's in the same direction, because the kernel read-ahead code detects sequential reads, whereas it doesn't when it goes backwards. The difference can be up to a factor of 10 for long index scans. Though... true... for a limit 1... it wouldn't matter that much. But it's become habit to match index sort order by now. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
