From: | Jan Wieck <JanWieck(at)Yahoo(dot)com> |
---|---|
To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
Cc: | Alessio Bragadini <alessio(at)albourne(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Changing Column Order (Was Re: MySQL vs PostgreSQL.) |
Date: | 2002-10-15 14:37:41 |
Message-ID: | 3DAC2835.2BA5CB60@Yahoo.com |
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Lists: | pgsql-general pgsql-hackers pgsql-jdbc |
Bruce Momjian wrote:
>
> Alessio Bragadini wrote:
> > On Sat, 2002-10-12 at 11:37, Gavin Sherry wrote:
> >
> > > I cannot think of any reason why changing column order should be
> > > implemented in Postgres. Seems like a waste of time/more code bloat for
> > > something which is strictly asthetic.
> > >
> > > Regardless, I do have collegues/clients who ask when such a feature will
> > > be implemented. Why is this useful?
> >
> > Has column ordering any effect on the physical tuple disposition? I've
> > heard discussions about keeping fixed-size fields at the beginning of
> > the tuple and similar.
> >
> > Sorry for the lame question. :-)
>
> Yes, column ordering matches physical column ordering in the file, and
> yes, there is a small penalty for accessing any columns after the first
> variable-length column (pg_type.typlen < 0). CHAR() used to be a fixed
> length column, but with TOAST (large offline storage) it became variable
> length too. I don't think there is much of a performance hit, though.
When was char() fixed size? We had fixed size things like char, char2,
char4 ... char16. But char() is internally bpchar() and has allways been
variable-length.
Jan
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