Subject: Re: [HACKERS] Custom compression methods
To: =?UTF-8?B?0JXQstCz0LXQvdC40Lkg0KjQuNGI0LrQuNC9?= <itparanoia@gmail.com>
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: <bc458704-578f-e824-9d28-3f060d95489a@2ndquadrant.com>
Date: Mon, 20 Nov 2017 16:29:11 +0100
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On 11/20/2017 04:21 PM, Евгений Шишкин wrote:
> 
> 
>> On Nov 20, 2017, at 18:18, Tomas Vondra <tomas.vondra@2ndquadrant.com
>> <mailto:tomas.vondra@2ndquadrant.com>> wrote:
>>
>>
>> I don't think we need to do anything smart here - it should behave just
>> like dropping a data type, for example. That is, error out if there are
>> columns using the compression method (without CASCADE), and drop all the
>> columns (with CASCADE).
> 
> 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.

But I'm wondering if ALTER COLUMN ... SET NOT COMPRESSED should do that
(currently it only disables compression for new data).


regards

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