Message-ID: <1115838416.428257d0e5bc3@webmail.telus.net>
Date: Wed, 11 May 2005 12:06:56 -0700
From: Mischa Sandberg <mischa.sandberg@telus.net>
To: pgsql-performance@postgresql.org
Subject: Re: Prefetch
References: <200505100652.51401.molson@oceanconsulting.com>
	<42818B2E.8060403@vilain.net>
	<42818FB1.4060403@familyhealth.com.au>
In-Reply-To: <42818FB1.4060403@familyhealth.com.au>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
User-Agent: Internet Messaging Program (IMP) 3.1-cvs

Quoting Christopher Kings-Lynne <chriskl@familyhealth.com.au>:

> > Another trick you can use with large data sets like this when you
> want 
> > results
> > back in seconds is to have regularly updated tables that aggregate
> the data
> > along each column normally aggregated against the main data set.
> 
> > Maybe some bright person will prove me wrong by posting some
> working
> > information about how to get these apparently absent features
> working.
> 
> Most people just use simple triggers to maintain aggregate summary
> tables...

Don't know if this is more appropriate to bizgres, but:
What the first poster is talking about is what OLAP cubes do.

For big aggregating systems (OLAP), triggers perform poorly, 
compared to messy hand-rolled code. You may have dozens
of aggregates at various levels. Consider the effect of having 
each detail row cascade into twenty updates. 

It's particularly silly-looking when data is coming in as 
batches of thousands of rows in a single insert, e.g.

   COPY temp_table FROM STDIN;
   UPDATE fact_table ... FROM ... temp_table
   INSERT INTO fact_table ...FROM...temp_table

   (the above pair of operations is so common, 
    Oracle added its "MERGE" operator for it).

Hence my recent post (request) for using RULES to aggregate 
--- given no luck with triggers "FOR EACH STATEMENT".