From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Teodor Sigaev <teodor(at)sigaev(dot)ru> |
Cc: | Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [PATCHES] GIN improvements |
Date: | 2008-07-24 18:29:58 |
Message-ID: | 9142.1216924198@sss.pgh.pa.us |
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Lists: | pgsql-hackers pgsql-patches |
Teodor Sigaev <teodor(at)sigaev(dot)ru> writes:
>> operations such as page splits. Do we need to change the planner to
>> assume that this only works nicely for btree?
> It seems to that direction (backward or forward) has meaning only for
> indexes with amcanorder = true. With amcanorder=false results will be
> occasionally for any direction.
Well, no; amcanorder specifies that the index can return results that
are sorted according to some externally meaningful ordering. The
question at hand is just whether the results of a single indexscan
are self-consistent. That's a property that can reasonably be expected
to hold regardless of amcanorder; it does hold for hash indexes for
instance. (In the case of hash we have to forbid splitting a bucket
that's actively being scanned in order to make it true.)
regards, tom lane
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