Subject: Re: Custom compression methods
To: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>,
 pgsql-hackers@postgresql.org
References: <20170907194236.4cefce96@wp.localdomain>
 <20170912175505.4afa11fd@wp.localdomain>
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Organization: 2ndQuadrant
Message-ID: <5c84382f-1065-e9e8-dde8-4c1f5ae1007b@2ndquadrant.com>
Date: Wed, 1 Nov 2017 17:05:58 -0400
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On 9/12/17 10:55, Ildus Kurbangaliev wrote:
>> The patch also includes custom compression method for tsvector which
>> is used in tests.
>>
>> [1]
>> https://www.postgresql.org/message-id/CAPpHfdsdTA5uZeq6MNXL5ZRuNx%2BSig4ykWzWEAfkC6ZKMDy6%3DQ%40mail.gmail.com
> Attached rebased version of the patch. Added support of pg_dump, the
> code was simplified, and a separate cache for compression options was
> added.

I would like to see some more examples of how this would be used, so we
can see how it should all fit together.

So far, it's not clear to me that we need a compression method as a
standalone top-level object.  It would make sense, perhaps, to have a
compression function attached to a type, so a type can provide a
compression function that is suitable for its specific storage.

The proposal here is very general: You can use any of the eligible
compression methods for any attribute.  That seems very complicated to
manage.  Any attribute could be compressed using either a choice of
general compression methods or a type-specific compression method, or
perhaps another type-specific compression method.  That's a lot.  Is
this about packing certain types better, or trying out different
compression algorithms, or about changing the TOAST thresholds, and so on?

Ideally, we would like something that just works, with minimal
configuration and nudging.  Let's see a list of problems to be solved
and then we can discuss what the right set of primitives might be to
address them.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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