Horton

Re: Custom compression methods

Peter Eisentraut <peter.eisentraut@2ndquadrant.com>

View thread View on postgr.es
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>, pgsql-hackers@postgresql.org
Date: 2017-11-01T21:05:58Z
Lists: pgsql-hackers 
On 9/12/17 10:55, Ildus Kurbangaliev wrote:
>> The patch also includes custom compression method for tsvector which
>> is used in tests.
>>
>> [1]
>> https://www.postgresql.org/message-id/CAPpHfdsdTA5uZeq6MNXL5ZRuNx%2BSig4ykWzWEAfkC6ZKMDy6%3DQ%40mail.gmail.com
> Attached rebased version of the patch. Added support of pg_dump, the
> code was simplified, and a separate cache for compression options was
> added.

I would like to see some more examples of how this would be used, so we
can see how it should all fit together.

So far, it's not clear to me that we need a compression method as a
standalone top-level object.  It would make sense, perhaps, to have a
compression function attached to a type, so a type can provide a
compression function that is suitable for its specific storage.

The proposal here is very general: You can use any of the eligible
compression methods for any attribute.  That seems very complicated to
manage.  Any attribute could be compressed using either a choice of
general compression methods or a type-specific compression method, or
perhaps another type-specific compression method.  That's a lot.  Is
this about packing certain types better, or trying out different
compression algorithms, or about changing the TOAST thresholds, and so on?

Ideally, we would like something that just works, with minimal
configuration and nudging.  Let's see a list of problems to be solved
and then we can discuss what the right set of primitives might be to
address them.

-- 
Peter Eisentraut              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.