Re: [HACKERS] Custom compression methods

Hi Ildus,

On 14.11.2017 16:23, Ildus Kurbangaliev wrote:
> On Thu, 2 Nov 2017 15:28:36 +0300 Ildus Kurbangaliev
> <i(dot)kurbangaliev(at)postgrespro(dot)ru> wrote:
>
>> On Tue, 12 Sep 2017 17:55:05 +0300 Ildus Kurbangaliev
>> <i(dot)kurbangaliev(at)postgrespro(dot)ru> wrote:
>>
>>>
>>> Attached rebased version of the patch. Added support of pg_dump,
>>> the code was simplified, and a separate cache for compression
>>> options was added.
>>>
>>
>> Attached version 3 of the patch. Rebased to the current master,
>> removed ALTER TYPE .. SET COMPRESSED syntax, fixed bug in
>> compression options cache.
>>
>
> Attached version 4 of the patch. Fixed pg_upgrade and few other
> bugs.
>

I've started to review your code. And even though it's fine overall I
have few questions and comments (aside from DROP COMPRESSION METHOD
discussion).

1. I'm not sure about proposed syntax for ALTER TABLE command:

>> ALTER TABLE t ALTER COLUMN a SET COMPRESSED <cmname> WITH
>> (<options>); ALTER TABLE t ALTER COLUMN a SET NOT COMPRESSED;

ISTM it is more common for Postgres to use syntax like SET/DROP for
column options (SET/DROP NOT NULL, DEFAULT etc). My suggestion would be:

ALTER TABLE t ALTER COLUMN a SET COMPRESSED USING <compression_method>
WITH (<options>);
ALTER TABLE t ALTER COLUMN a DROP COMPRESSED;

(keyword USING here is similar to "CREATE INDEX ... USING <method>" syntax)

2. The way you changed DefineRelation() implies that caller is
responsible for creation of compression options. Probably it would be
better to create them within DefineRelation().

3. Few minor issues which seem like obsolete code:

Function freeRelOptions() is defined but never used.

Function getBaseTypeTuple() has been extracted from
getBaseTypeAndTypmod() but never used separately.

In toast_flatten_tuple_to_datum() there is untoasted_value variable
which is only used for meaningless assignment.

(Should I send a patch for that kind of issues?)

--
Ildar Musin
i(dot)musin(at)postgrespro(dot)ru