On Tue, 2009-05-19 at 08:58 -0400, Tom Lane wrote: > Simon Riggs <simon@xxxxxxxxxxxxxxx> writes: > > Both plans for this query show an IndexScan on a two column-index, with > > an Index Condition of equality on the leading column. The ORDER BY > > specifies a sort by the second index column, so the top-level Sort is > > superfluous in this case. > > > My understanding is that we don't currently eliminate superfluous > > additional sorts of this kind. > > Nonsense. The planner might think some other plan is cheaper, but > it definitely knows how to do this, and has since at least 8.1. Please look at Dimitri's plan. If it can remove the pointless sort, why does it not do so? I agree that it will remove a Sort when the data is already has the exact same interesting sort order. In this case the sort order is not exactly the same, but looks fully removable to me. -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
