Horton

Re: [HACKERS] Custom compression methods

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Ildar Musin <i.musin@postgrespro.ru>
Date: 2017-12-01T21:06:00Z
Lists: pgsql-hackers 
On 12/01/2017 08:20 PM, Robert Haas wrote:
> On Fri, Dec 1, 2017 at 10:18 AM, Tomas Vondra
> <tomas.vondra@2ndquadrant.com> wrote:
>> It has very little impact on this patch, as it has nothing to do with
>> columnar storage. That is, each value is compressed independently.
> 
> I understand that this patch is not about columnar storage, but I 
> think the idea that we may want to operate on the compressed data 
> directly is not only applicable to that case.
> 

Yeah. To clarify, my point was that column stores benefit from
compressing many values at once, and then operating on this compressed
vector. That is not what this patch is doing (or can do), of course.

But I certainly do agree that if the compression can be integrated into
the data type, allowing processing on compressed representation, then
that will beat whatever this patch is doing, of course ...

>>
>> I agree with these thoughts in general, but I'm not quite sure
>> what is your conclusion regarding the patch.
> 
> I have not reached one. Sometimes I like to discuss problems before 
> deciding what I think. :-)
> 

That's lame! Let's make decisions without discussion ;-)

>
> It does seem to me that the patch may be aiming at a relatively narrow
> target in a fairly large problem space, but I don't know whether to
> label that as short-sightedness or prudent incrementalism.
> 

I don't know either. I don't think people will start switching their
text columns to lz4 just because they can, or because they get 4% space
reduction compared to pglz.

But the ability to build per-column dictionaries seems quite powerful, I
guess. And I don't think that can be easily built directly into JSONB,
because we don't have a way to provide information about the column
(i.e. how would you fetch the correct dictionary?).


regards

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

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.