Subject: Re: [HACKERS] Custom compression methods
To: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>,
 Robert Haas <robertmhaas@gmail.com>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>,
 Tomas Vondra <tomas.vondra@2ndquadrant.com>,
 Alvaro Herrera <alvherre@2ndquadrant.com>,
 =?UTF-8?B?0JXQstCz0LXQvdC40Lkg0KjQuNGI0LrQuNC9?= <itparanoia@gmail.com>,
 Andres Freund <andres@anarazel.de>, Oleg Bartunov <obartunov@gmail.com>,
 Craig Ringer <craig@2ndquadrant.com>,
 Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
 Chapman Flack <chap@anastigmatix.net>
References: <20171201194859.le5hvnnrjzhxhm2t@alvherre.pgsql>
 <bc4e4595-24c5-c2eb-323e-9f31e9c98140@2ndquadrant.com>
 <20171206180716.75ba9ba9@postgrespro.ru>
 <CA+TgmobjDLp5xxodzN+TwhuhdQxM3wJw6AaLatDaBgPQm+N+kw@mail.gmail.com>
 <20171211155555.05ddd2fc@postgrespro.ru>
 <CA+Tgmoa7U9Pgc8YV-eRkKAK2s74aL6Yw1Wsj81PTjyrn0Eg99g@mail.gmail.com>
 <CAPpHfdsO0wSy6ZEoOQS5AkxTRXeCzv4uz=S8hOOJNgOxPmJW4A@mail.gmail.com>
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 <CA+TgmoZqJYP+othk0c-r6acjVWWvBoxkWm5eHLUE=8VyezQKKw@mail.gmail.com>
 <20171213151818.75a20259@postgrespro.ru>
 <CA+TgmoZ68LyL0rFPDgC1J-6p9ZQZc2xS4Txd-9661s+w6_MwBg@mail.gmail.com>
 <20171218115431.2b3e29ba@wp.localdomain> <20180115024930.48583c69@hh>
From: Ildar Musin <i.musin@postgrespro.ru>
Message-ID: <0633c6e5-5328-5c5b-708b-c4409e3fd131@postgrespro.ru>
Date: Mon, 22 Jan 2018 23:26:31 +0300
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Hello Ildus,


15/01/2018 00:49, Ildus Kurbangaliev пишет:
> Attached a new version of the patch. Main changes:
>
> * compression as an access method
> * pglz as default compression access method.
> * PRESERVE syntax for tables rewrite control.
> * pg_upgrade fixes
> * support partitioned tables.
> * more tests.
>
You need to rebase to the latest master, there are some conflicts. I've
applied it to the three days old master to try it.

As I can see the documentation is not yet complete. For example, there
is no section for ALTER COLUMN ... SET COMPRESSION in ddl.sgml; and
section "Compression Access Method Functions" in compression-am.sgml
hasn't been finished.

I've implemented an extension [1] to understand the way developer would
go to work with new infrastructure. And for me it seems clear. (Except
that it took me some effort to wrap my mind around varlena macros but it
is probably a different topic).

I noticed that you haven't cover 'cmdrop' in the regression tests and I
saw the previous discussion about it. Have you considered using event
triggers to handle the drop of column compression instead of 'cmdrop'
function? This way you would kill two birds with one stone: it still
provides sufficient infrastructure to catch those events (and it
something postgres already has for different kinds of ddl commands) and
it would be easier to test.

Thanks!

[1] https://github.com/zilder/pg_lz4

-- 
Ildar Musin
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company