"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). What I wonder is what the optimal thing to do really is if a level doesn't fit in memory. Is it best to do a disk sort just of that level and then return to accumulating levels one by one in memory? Or is it best to fail over to a single disk sort of all the remaining tuples? Also, I wonder how expensive checking the level break key on every tuple will be. I don't think it invalidates the approach but it has to be taken into account. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's RemoteDBA services! -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
