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Re: column updates

From: Martijn van Oosterhout <kleptog(at)svana(dot)org>
To: Ben <bench(at)silentmedia(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: column updates
Date: 2004-10-29 21:54:05
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-general
The number of dead tuples is the number of UPDATE statements you make.
You if you just do a straight UPDATE x set f1=x, f2=y, ... that will be
as optimal as you can get.

The only exception may be toasted fields, which would only apply if you
had fields with more than 2K of data or so...

Hope this helps,

On Fri, Oct 29, 2004 at 12:24:35PM -0700, Ben wrote:
> I'm designing a system where I'll be making frequent updates to rows, but
> some columns will change far less frequently than others. All columns will 
> be read with equal frequency, though probably by means of a materialized 
> view. Updates will happen via a stored proc.
> Which makes the most sense?
> 1. Blindly overwrite the value for all columns, even columns that haven't
> changed.
> 2. Compare the current value and update each column at a time, leaving 
> unchanged columns alone.
> 3. Break out my tables more, so that infrequently updated columns are in 
> different tables. 
> I'm thinking that 1 and 2 are similar and less complex than 3, but might 
> result in more dead tuples. 2 and 3 will have to look up values before 
> updates can happen. I don't know if 2 has any advantage over 1. 1 is 
> certainly the simpliest.
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Martijn van Oosterhout   <kleptog(at)svana(dot)org>
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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