Re: [HACKERS] Cube extension point support // GSoC'13

From: Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Stas Kelvich <stas(dot)kelvich(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, pgsql-students(at)postgresql(dot)org
Subject: Re: [HACKERS] Cube extension point support // GSoC'13
Date: 2013-10-21 22:00:24
Message-ID: m28uxmthc7.fsf@2ndQuadrant.fr
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Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> I believe the reason GIST has compress/decompress functions is not for
> TOAST (they predate that, if memory serves), but to allow the on-disk
> representation of an index entry to be different from the data type's
> normal representation in other ways --- think lossy storage in particular.

My understanding of the use case for those functions is to do with
storing a different data type in the index upper nodes and in the index
leafs. It should be possible to do that in a non-lossy way, so that you
would implement compress/decompress and not declare the RECHECK bits.

Then again I'm talking from 8.3 era memories of when I tried to
understand GiST enough to code the prefix extension.

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support

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