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Re: TOAST usage setting

From: "Zeugswetter Andreas ADI SD" <ZeugswetterA(at)spardat(dot)at>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>,"Gregory Stark" <stark(at)enterprisedb(dot)com>
Cc: "Bruce Momjian" <bruce(at)momjian(dot)us>,<pgsql-hackers(at)postgresql(dot)org>
Subject: Re: TOAST usage setting
Date: 2007-05-30 16:10:28
Message-ID: E1539E0ED7043848906A8FF995BDA579021B2BBB@m0143.s-mxs.net (view raw or flat)
Thread:
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

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