Re: GIN improvements part2: fast scan

From: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
To: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Cc: Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: GIN improvements part2: fast scan
Date: 2014-03-13 16:58:32
Message-ID: 5321E3B8.8040809@vmware.com
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On 03/12/2014 07:52 PM, Alexander Korotkov wrote:
>> >
>> >* I just noticed that the dummy trueTriConsistentFn returns GIN_MAYBE,
>> >rather than GIN_TRUE. The equivalent boolean version returns 'true' without
>> >recheck. Is that a typo, or was there some reason for the discrepancy?
>> >
> Actually, there is not difference in current implementation, But I
> implemented it so that trueTriConsistentFn can correctly work
> with shimBoolConsistentFn. In this case it should return GIN_MAYBE in case
> when it have no GIN_MAYBE in the input (as analogue of setting recheck
> flag). So, it could return GIN_TRUE only if it checked that input has
> GIN_MAYBE. However, checking would be just wasting of cycles. So I end up
> with just GIN_MAYBE :-)

I don't understand that. As it is, it's inconsistent with the boolean
trueConsistent function. trueConsistent always returns TRUE with
recheck=false. And in GIN_SEARCH_MODE_EVERYTHING mode, there are no
regular scan keys.

- Heikki

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