Subject: Re: [HACKERS] Custom compression methods
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Cc: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>,
 Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>,
 Oleg Bartunov <obartunov@gmail.com>, Craig Ringer <craig@2ndquadrant.com>,
 Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>
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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <641e18b7-1bb6-ba8d-fddb-d0259f970897@2ndquadrant.com>
Date: Mon, 20 Nov 2017 17:31:45 +0100
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On 11/20/2017 04:43 PM, Евгений Шишкин wrote:
> 
> 
>> On Nov 20, 2017, at 18:29, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
>>
>>>
>>> What about instead of dropping column we leave data uncompressed?
>>>
>>
>> That requires you to go through the data and rewrite the whole table.
>> And I'm not aware of a DROP command doing that, instead they just drop
>> the dependent objects (e.g. DROP TYPE, ...). So per PLOS the DROP
>> COMPRESSION METHOD command should do that too.
> 
> Well, there is no much you can do with DROP TYPE. But i'd argue that compression
> is different. We do not drop data in case of DROP STATISTICS or DROP INDEX.
> 

But those DROP commands do not 'invalidate' data in the heap, so there's
no reason to drop the columns.

> At least there should be a way to easily alter compression method then.
> 

+1


regards

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