Date: Tue, 13 Apr 2010 15:22:26 -0400
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Lewis Kapell <lkapell@setonhome.org>
Cc: pgsql-admin@postgresql.org
Subject: Re: TOAST behavior in 8.3 and 8.4
Message-ID: <20100413192226.GE2990@alvh.no-ip.org>
References: <4BC4BBD4.40706@setonhome.org>
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Lewis Kapell wrote:
> I have a table with a text column, wherein most values range between
> 800 and 1700 bytes.  The data should be highly compressible, however
> these values appear to be too small to trigger the TOAST mechanism -
> I understand the default value of TOAST_TUPLE_THRESHOLD is about
> 2kb.


> However, I checked to see whether the behavior of TOAST had been
> changed in 8.4, since I am hoping to upgrade soon.  I found the
> following comment in the release notes:
> 
> "Consider TOAST compression on values as short as 32 bytes
> (previously 256 bytes)"

The 2kB are compared against tuple size.  The 32 bytes (previously 256)
are compared against a single column value.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support