2010/8/19 David Fetter <da...@fetter.org>: > On Thu, Aug 19, 2010 at 12:45:13PM +0200, Pavel Stehule wrote: >> Hello >> >> > I'll test both variant first. Maybe there are not any significant >> > difference between them. Now nodeAgg can build, fill a tuplesort. >> > So I think is natural use it. It needs only one - skip a calling a >> > transident function and directly call final function with external >> > tuplesort. Minimally you don't need 2x same code. >> >> yesterday I did a small test. Aggregates without transident >> functions are only about 2% faster, so there has no sense thinking >> more about them. I'll send a patch with median and percentile >> functions immediately - these functions are implemented like usual >> aggregates. > > NTILE is already a windowing function. Might want to check into any > performance improvements you can give that.
The performance has to be +/- same. It is based on same technology - tuplesort. > > As to median, please make sure you say in detail which median you're > using and name it so, as there is no single, authoritative median. I searched about this. And I found so there is a different methods for same statistic value with different names. But result has to be same. I don't found a other median than "arithmetic" or "financial" median (with a two derived forms - left, right median). These methods are a different forms of some SQL - see http://www.simple-talk.com/sql/t-sql-programming/median-workbench/ and it is SQL related solutions. With tuplesort I can to use a simple solution - I have a number of elements, have a sorted set and can move to n position is set. Next forms of median what I found are estimations. regards Pavel > > Cheers, > David. > -- > David Fetter <da...@fetter.org> http://fetter.org/ > Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter > Skype: davidfetter XMPP: david.fet...@gmail.com > iCal: webcal://www.tripit.com/feed/ical/people/david74/tripit.ics > > Remember to vote! > Consider donating to Postgres: http://www.postgresql.org/about/donate > -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
