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Date: Wed, 6 Dec 2017 18:07:16 +0300
From: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, =?UTF-8?B?0JXQstCz0LXQvdC4?=
 =?UTF-8?B?0Lkg0KjQuNGI0LrQuNC9?= <itparanoia@gmail.com>, 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>
Subject: Re: [HACKERS] Custom compression methods
Message-ID: <20171206180716.75ba9ba9@postgrespro.ru>
In-Reply-To: <bc4e4595-24c5-c2eb-323e-9f31e9c98140@2ndquadrant.com>
References: <20171201194859.le5hvnnrjzhxhm2t@alvherre.pgsql>
	<bc4e4595-24c5-c2eb-323e-9f31e9c98140@2ndquadrant.com>
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Precedence: bulk

On Fri, 1 Dec 2017 21:47:43 +0100
Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
 
> 
> +1 to do the rewrite, just like for other similar ALTER TABLE commands

Ok. What about the following syntax:

ALTER COLUMN DROP COMPRESSION - removes compression from the column
with the rewrite and removes related compression options, so the user
can drop compression method.

ALTER COLUMN SET COMPRESSION NONE for the cases when
the users want to just disable compression for future tuples. After
that they can keep compressed tuples, or in the case when they have a
large table they can decompress tuples partially using e.g. UPDATE,
and then use ALTER COLUMN DROP COMPRESSION which will be much faster
then.

ALTER COLUMN SET COMPRESSION <cm> WITH <cmoptions> will change
compression for new tuples but will not touch old ones. If the users
want the recompression they can use DROP/SET COMPRESSION combination.

I don't think that SET COMPRESSION with the rewrite of the whole table
will be useful enough on any somewhat big tables and same time big
tables is where the user needs compression the most.

I understand that ALTER with the rewrite sounds logical and much easier
to implement (and it doesn't require Oids in tuples), but it could be
unusable.

-- 
----
Regards,
Ildus Kurbangaliev