From: | Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com> |
---|---|
To: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
Cc: | Phil Currier <pcurrier(at)gmail(dot)com>, "Florian G(dot) Pflug" <fgp(at)phlo(dot)org>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Column storage positions |
Date: | 2007-02-21 19:27:05 |
Message-ID: | 20070221111923.U81529@megazone.bigpanda.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Wed, 21 Feb 2007, Martijn van Oosterhout wrote:
> On Wed, Feb 21, 2007 at 12:06:30PM -0500, Phil Currier wrote:
> > Well, for two reasons:
> >
> > 1) If you have a table with one very-frequently-accessed varchar()
> > column and several not-frequently-accessed int columns, it might
> > actually make sense to put the varchar column first. The system won't
> > always be able to make the most intelligent decision about table
> > layout.
>
> Umm, the point of the exercise is that if you know there are int
> columns, then you can skip over them, whereas you can never skip over a
> varchar column. So there isn't really any situation where it would be
> better to put the varchar first.
IIRC, in the first message in this thread, or another recent thread of
this type, someone tried a reordering example with alternating
smallints and varchar() and found that the leftmost varchar was
actually slower to access after reordering, so I'm not sure that we can
say there isn't a situation where it would affect things.
From | Date | Subject | |
---|---|---|---|
Next Message | Florian G. Pflug | 2007-02-21 19:29:06 | Re: Column storage positions |
Previous Message | Simon Riggs | 2007-02-21 18:54:43 | Re: HOT for PostgreSQL 8.3 |