Horton

Re: [HACKERS] Custom compression methods

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, Justin Pryzby <pryzby@telsasoft.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Alexander Korotkov <a.korotkov@postgrespro.ru>, David Steele <david@pgmasters.net>, Ildus Kurbangaliev <i.kurbangaliev@gmail.com>, Dmitry Dolgov <9erthalion6@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-19T22:38:43Z
Lists: pgsql-hackers

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On 2021-Mar-19, Robert Haas wrote:

> On Fri, Mar 19, 2021 at 10:11 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > Also added a test case for vacuum full to recompress the data.
> 
> I committed the core patch (0003) with a bit more editing.  Let's see
> what the buildfarm thinks.

I updated the coverage script to use --with-lz4; results are updated.
While eyeballing the results I noticed this bit in
lz4_decompress_datum_slice():

+   /* slice decompression not supported prior to 1.8.3 */
+   if (LZ4_versionNumber() < 10803)
+       return lz4_decompress_datum(value);

which I read as returning the complete decompressed datum if slice
decompression is not supported.  I thought that was a bug, but looking
at the caller I realize that this isn't really a problem, since it's
detoast_attr_slice's responsibility to slice the result further -- no
bug, it's just wasteful.  I suggest to add comments to this effect,
perhaps as the attached (feel free to reword, I think mine is awkward.)

-- 
Álvaro Herrera                            39°49'30"S 73°17'W
Si no sabes adonde vas, es muy probable que acabes en otra parte.

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.