From: Tom Lane <tgl@sss.pgh.pa.us>
To: Teodor Sigaev <teodor@sigaev.ru>
Cc: Pgsql Hackers <pgsql-hackers@postgresql.org>
Subject: Re: [PATCHES] GIN improvements
Date: Thu, 24 Jul 2008 14:29:58 -0400
Message-ID: <9142.1216924198@sss.pgh.pa.us> (raw)
In-Reply-To: <4888C90B.3020704@sigaev.ru>
References: <483FD205.4090904@sigaev.ru>
<486BC501.6060605@sigaev.ru>
<27880.1215810535@sss.pgh.pa.us>
<487A6E0C.3090600@sigaev.ru>
<8993.1216843701@sss.pgh.pa.us>
<4888A594.6010102@sigaev.ru>
<7913.1216918895@sss.pgh.pa.us>
<8177.1216920042@sss.pgh.pa.us>
<4888C90B.3020704@sigaev.ru>
Teodor Sigaev <teodor@sigaev.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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To: pgsql-patches@postgresql.org
Cc: tgl@sss.pgh.pa.us, teodor@sigaev.ru, pgsql-hackers@postgresql.org
Subject: Re: [PATCHES] GIN improvements
In-Reply-To: <9142.1216924198@sss.pgh.pa.us>
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