On Thu, 2008-03-20 at 22:35 +0000, Gregory Stark wrote: > "Simon Riggs" <[EMAIL PROTECTED]> writes: > > > If we assume we use heap sort, then if we *know* that the data is > > presorted on (a) then we should be able to emit tuples directly that the > > value of (a) changes and keep emitting them until the heap is empty, > > since they will exit the heap in (a,b) order. > > Actually, I would think the way to do this would be to do a quicksort if you > find you've accumulated all the records in a subgroup in memory. One easy way > to do it would be to have nodeSort build a new tuplesort for each subgroup if > it has a level break key parameter set (memories of RPG III are coming > bubbling to the surface).
Yes, its essentially the same thing as running a series of otherwise unconnected sorts. However, that seems to introduce its own overheads if we did that literally. We needn't fix this to either a heapsort or a quicksort. We can let the existing code decide which and let the mode change naturally from one to the other as is needed. -- Simon Riggs 2ndQuadrant http://www.2ndQuadrant.com PostgreSQL UK 2008 Conference: http://www.postgresql.org.uk -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
