Date: Tue, 16 Nov 2010 12:28:16 +0100
From: Louis-David Mitterrand <vindex+lists-pgsql-performance@apartia.org>
To: pgsql-performance@postgresql.org
Subject: Re: best db schema for time series data?
Message-ID: <20101116112816.GA2953@apartia.fr>
Mail-Followup-To: pgsql-performance@postgresql.org
References: <20101116105055.GA26129@apartia.fr>
 <4CE2688B.2050000@tweakers.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4CE2688B.2050000@tweakers.net>
User-Agent: Mutt/1.5.21 (2010-09-15)

On Tue, Nov 16, 2010 at 12:18:35PM +0100, Arjen van der Meijden wrote:
> On 16-11-2010 11:50, Louis-David Mitterrand wrote:
> >I have to collect lots of prices from web sites and keep track of their
> >changes. What is the best option?
> >
> >1) one 'price' row per price change:
> >
> >	create table price (
> >		id_price primary key,
> >		id_product integer references product,
> >		price integer
> >	);
> >
> >2) a single 'price' row containing all the changes:
> >
> >	create table price (
> >		id_price primary key,
> >		id_product integer references product,
> >		price integer[] -- prices are 'pushed' on this array as they change
> >	);
> >
> >Which is bound to give the best performance, knowing I will often need
> >to access the latest and next-to-latest prices?
> 
> If you mostly need the last few prices, I'd definitaly go with the
> first aproach, its much cleaner. Besides, you can store a date/time
> per price, so you know when it changed. With the array-approach
> that's a bit harder to do.
> 
> If you're concerned with performance, introduce some form of a
> materialized view for the most recent price of a product. Or reverse
> the entire process and make a "current price"-table and a "price
> history"-table.

That's exactly my current 'modus operandi'. So it's nice to have
confirmation that I'm not using the worst schema out there :)