Re: TOAST usage setting

Zeugswetter Andreas DCP SD <zeugswettera@spardat.at>

From: "Zeugswetter Andreas ADI SD" <ZeugswetterA@spardat.at>
To: "Tom Lane" <tgl@sss.pgh.pa.us>, "Gregory Stark" <stark@enterprisedb.com>
Cc: "Bruce Momjian" <bruce@momjian.us>, <pgsql-hackers@postgresql.org>
Date: 2007-05-30T16:10:28Z
Lists: pgsql-hackers
> > Whereas if you set toast_tuples_per_page to 8k then the only option 
> > for Postgres will be to put each datum in its own page and 
> waste 1-3k 
> > on every page.
> 
> No, because actually the code is designed to make the toast 
> chunk size just enough less than 8K that the tuples fit.

He mentioned toasted values of 6-7k each. If all values are of that size
(like payment slip tiffs) there is nothing we would do with the
remaining 1-2k on each page. But that disadvantage disappears as soon as
you have just a little more variability in the length. Still, it might
be enough to opt for some freespace reuse smarts if we can think of a
cheap heuristic. But the cost to fetch such a "distributed" tuple would
be so huge I doubt there is anything to win but disk space.

Andreas