Re: TOAST usage setting

Zeugswetter Andreas DCP SD <zeugswettera@spardat.at>

From: "Zeugswetter Andreas ADI SD" <ZeugswetterA@spardat.at>
To: "Bruce Momjian" <bruce@momjian.us>, <pgsql-hackers@postgresql.org>
Cc: "Gregory Stark" <stark@enterprisedb.com>, "Tom Lane" <tgl@sss.pgh.pa.us>
Date: 2007-05-30T11:04:33Z
Lists: pgsql-hackers
> I reran the tests with hashtext(), and created a SUMMARY.HTML chart:
> 
> 	http://momjian.us/expire/TOAST/
> 
> What you will see is that pushing TEXT to a TOAST column 
> allows quick access to non-TOAST values and single-row TOAST 
> values, but accessing all TOAST columns is slower than 
> accessing them in the heap, by a factor of 3-18x.

Um, my understanding for this measurement would be to tweak
TOAST_TUPLE_THRESHOLD, and use a fixed TOAST_MAX_CHUNK_SIZE ?
Why would you want to increase the number of toast tuples required for
one column value ?

My expectation would be, that we want to allow a toast tuple to fill a
whole page (TOAST_TUPLES_PER_PAGE = 1),
but keep or reduce the threshold. Maybe we need other logic to find and
use free space for that, though (8.4 material).

Andreas