Horton

Re: [HACKERS] Custom compression methods

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-12-14T15:21:44Z
Lists: pgsql-hackers 
On Wed, Dec 13, 2017 at 5:10 AM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
>> 2. If several data types can benefit from a similar approach, it has
>> to be separately implemented for each one.
>
> I don't think the current solution improves that, though. If you want to
> exploit internal features of individual data types, it pretty much
> requires code customized to every such data type.
>
> For example you can't take the tsvector compression and just slap it on
> tsquery, because it relies on knowledge of internal tsvector structure.
> So you need separate implementations anyway.

I don't think that's necessarily true.  Certainly, it's true that *if*
tsvector compression depends on knowledge of internal tsvector
structure, *then* that you can't use the implementation for anything
else (this, by the way, means that there needs to be some way for a
compression method to reject being applied to a column of a data type
it doesn't like).  However, it seems possible to imagine compression
algorithms that can work for a variety of data types, too.  There
might be a compression algorithm that is theoretically a
general-purpose algorithm but has features which are particularly
well-suited to, say, JSON or XML data, because it looks for word
boundaries to decide on what strings to insert into the compression
dictionary.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.