From: | "Zeugswetter Andreas ADI SD" <ZeugswetterA(at)spardat(dot)at> |
---|---|
To: | "Bruce Momjian" <bruce(at)momjian(dot)us>, <pgsql-hackers(at)postgresql(dot)org> |
Cc: | "Gregory Stark" <stark(at)enterprisedb(dot)com>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Subject: | Re: TOAST usage setting |
Date: | 2007-05-30 11:04:33 |
Message-ID: | E1539E0ED7043848906A8FF995BDA579021B2AE2@m0143.s-mxs.net |
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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
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