From: | Zeugswetter Andreas SB <ZeugswetterA(at)wien(dot)spardat(dot)at> |
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To: | "'Bruce Momjian'" <pgman(at)candle(dot)pha(dot)pa(dot)us>, Jan Wieck <JanWieck(at)Yahoo(dot)com> |
Cc: | PostgreSQL HACKERS <pgsql-hackers(at)postgresql(dot)org> |
Subject: | AW: TOAST & vacuum |
Date: | 2000-07-27 08:21:47 |
Message-ID: | 11C1E6749A55D411A9670001FA687963368032@sdexcsrv1.f000.d0188.sd.spardat.at |
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Lists: | pgsql-hackers |
> > TOAST is now vacuum-safe. When needed, the toaster creates a
> > second heap tuple, containing only plain or compressed
> > values. This one is then returned by the heap access methods
> > to the caller, so indices will never contain external
> > references.
> >
> > The changes are covered by #ifdef TOAST_INDICES, so can
> > easily be disabled at the time we have file versioning and
> > can recreate indices during vacuum.
>
> Seems this has some performance advantages. Un-toasting to traverse a
> btree index would be pretty slow. This way, it is all in the index.
Yes, but it limits the key size. I was suggesting to Jan, that he reconsider
the "toast choice made for the heap tuple" for each index key, and store the
key
compressed if it fits into 1/4 page.
I think the current setup (index toasting disabled) must be a lot better
performance
wise than if you enable the current "index toasting" state of things.
Andreas
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