Re: reducing NUMERIC size for 9.1

From: Richard Huxton <dev(at)archonet(dot)com>
To: Brendan Jurd <direvus(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: reducing NUMERIC size for 9.1
Date: 2010-07-16 12:51:23
Message-ID: 4C4055CB.8070801@archonet.com
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On 16/07/10 13:44, Brendan Jurd wrote:
>
> pg_column_size() did return the results I was expecting.
> pg_column_size(0::numeric) is 8 bytes on 8.4 and it's 6 bytes on HEAD
> with your patch.

> At this scale we should be seeing around 2 million bytes saved, but
> instead the tables are identical. Is there some kind of disconnect in
> how the new short numeric is making it to the disk, or perhaps another
> effect interfering with my test?

You've probably got rows being aligned to a 4-byte boundary. You're
probably not going to see any change unless you have a couple of 1-byte
columns that get placed after the numeric. If you went from 10 bytes
down to 8, that should be visible.

--
Richard Huxton
Archonet Ltd

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