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Re: TOAST usage setting

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Zeugswetter Andreas ADI SD <ZeugswetterA(at)spardat(dot)at>
Cc: "Jim C(dot) Nasby" <decibel(at)decibel(dot)org>, Gregory Stark <stark(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: TOAST usage setting
Date: 2007-06-06 03:27:25
Message-ID: (view raw or whole thread)
Lists: pgsql-hackers
Zeugswetter Andreas ADI SD wrote:
> > > The big question is do we want to drop the target tuple  size down
> to 
> > > 512, and increase the chunk size to 8k for 8.3?  Dropping the tuple 
> > > size down to 512 is going to give us some smaller TOAST values to
> fill 
> > > in free space created by the 8k chuck size, assuming you have both 
> > > types of values in the table.  Do we want to increase the access
> time 
> > > of long TOAST by 6% if it means having more wasted space for lots of
> > > 4.1k values?
> > 
> > If we do that people could see their disk space usage increase by up
> to
> > 16x: currently 513 bytes fits in heap and takes (roughly) 513 
> > bytes;
> No, you misunderstood. Bruce was suggesting changing the target to 512.
> That means if a row is wider than ~2k, toaster will try to toast until
> the base row is
> ~512 bytes. I would not do that part for 8.3. 

OK, what do you suggest for 8.3?  Attached are my suggestion to use 512
and a 4k chunk size, which I think means that 2.7k is the worst values
that has a loss of around 25%.

  Bruce Momjian  <bruce(at)momjian(dot)us>

  + If your life is a hard drive, Christ can be your backup. +

Attachment: /pgpatches/toast_values
Description: text/x-diff (1.4 KB)

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