Horton

Re: [HACKERS] Custom compression methods

Ildar Musin <i.musin@postgrespro.ru>

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From: Ildar Musin <i.musin@postgrespro.ru>
To: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>, pgsql-hackers@postgresql.org
Date: 2017-11-16T15:09:37Z
Lists: pgsql-hackers 
Hi Ildus,

On 14.11.2017 16:23, Ildus Kurbangaliev wrote:
> On Thu, 2 Nov 2017 15:28:36 +0300 Ildus Kurbangaliev
> <i.kurbangaliev@postgrespro.ru> wrote:
>
>> On Tue, 12 Sep 2017 17:55:05 +0300 Ildus Kurbangaliev
>> <i.kurbangaliev@postgrespro.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.musin@postgrespro.ru

Commits

  1. docs: Update TOAST storage docs for configurable compression.

  2. Further tweaking of pg_dump's handling of default_toast_compression.

  3. Fix interaction of TOAST compression with expression indexes.

  4. Tidy up more loose ends related to configurable TOAST compression.

  5. Short-circuit slice requests that are for more than the object's size.

  6. Mostly-cosmetic adjustments of TOAST-related macros.

  7. Remove useless configure probe for <lz4/lz4.h>.

  8. Error on invalid TOAST compression in CREATE or ALTER TABLE.

  9. docs: Fix omissions related to configurable TOAST compression.

  10. More code cleanup for configurable TOAST compression.

  11. Bring configure support for LZ4 up to snuff.

  12. Make compression.sql regression test independent of default.

  13. Use valid compression method in brin_form_tuple

  14. Fix up pg_dump's handling of per-attribute compression options.

  15. Allow configurable LZ4 TOAST compression.

  16. Fix inconsistencies in the code

  17. Mostly-cosmetic improvements in memory chunk header alignment coding.

  18. Allow numeric to use a more compact, 2-byte header in many cases.