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Re: Speeding up aggregates

From: Hannu Krosing <hannu(at)tm(dot)ee>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Speeding up aggregates
Date: 2002-12-06 21:49:58
Message-ID: 1039211397.2067.18.camel@rh72.home.ee (view raw or flat)
Thread:
Lists: pgsql-performance
Hannu Krosing kirjutas L, 07.12.2002 kell 02:32:
> Tom Lane kirjutas L, 07.12.2002 kell 01:46:
> > "Josh Berkus" <josh(at)agliodbs(dot)com> writes:
> > > What have other Postgres users done to speed up aggregates on large
> > > tables?
> > 
> > FWIW, I've implemented hashed aggregation in CVS tip.
> 
> Great! 
> 
> This should also make it easier to implement all kinds of GROUP BY
> ROLLUP|CUBE|GROUPING SETS|() queries.

Of these only ROLLUP can be done in one scan after sort, all others
would generally require several scans without hashing.


I just noticed that we don't even have a TODO for this. I think this
would be a good TODO item.

Bruce, could you add:

* Add ROLLUP, CUBE, GROUPING SETS options to GROUP BY


They are all defined in SQL99 p.79 <group by clause>


Some more background info (from a quick Google search)

a very short overview:
  http://www.neddo.com/dm3e/sql3&olap.html


more thorough guide for DB2:
http://www.student.math.uwaterloo.ca/~cs448/db2_doc/html/db2s0/frame3.htm#db2s0279


-----------------
Hannu


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