On Sat, 2007-01-20 at 13:36 +0000, Gregory Stark wrote: > "Alvaro Herrera" <[EMAIL PROTECTED]> writes: > > > Simon Riggs wrote: > > > >> I'm working on modifying Tuplestore that will allow you to store the > >> last N tuples, rather than all previous input. This is specifically > >> designed to allow Merge Join to do Mark/Restore without materializing > >> the whole sort set. This can also be used to materialize Windows (i.e. > >> <window clause> in SQL:2003), so you can store the current row plus n > >> PRECEDING and/or n FOLLOWING rows as appropriate. > > > > Interesting. This could also be used to implement the "partial sort" > > stuff that Oleg is so interested in, and in which I believe Greg Stark > > was also interested. > > I already have that implemented in tuplesort. The place where I was asking for > more guidance was at higher levels. How to communicate this information down > to the Sort node. > > It's not exactly the same as this case where you want to control when the old > tuples are purged though. I think the SORT LIMIT case is simpler since it you > just have to tell the tuplesort how many tuples you're interested in and it > can take care of pruning irrelevant tuples as it goes.
It does sound the same, but I think Greg is right: Sort Limit optimises the sort itself, not how the processing is handled following the Sort. Both approaches are required, for different cases. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
