| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net>, "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Reducing the overhead of NUMERIC data |
| Date: | 2005-11-03 14:49:09 |
| Message-ID: | 1131029349.8300.1925.camel@localhost.localdomain |
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| Lists: | pgsql-hackers pgsql-patches |
On Thu, 2005-11-03 at 11:13 -0300, Alvaro Herrera wrote:
> Simon Riggs wrote:
> > On PostgreSQL, CHAR(12) is a bpchar datatype with all instantiations of
> > that datatype having a 4 byte varlena header. In this example, all of
> > those instantiations having the varlena header set to 12, so essentially
> > wasting the 4 byte header.
>
> We need the length word because the actual size in bytes is variable,
> due to multibyte encoding considerations.
Succinctly put, thanks.
Incidentally, you remind me that other databases do *not* vary the
character length, even if they do have varying length UTF-8 within them.
So if you define CHAR(255) then it could blow up at a random length if
you store UTF-8 within it.
That's behaviour that I could never sanction, so I'll leave this now.
Best Regards, Simon Riggs
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