Horton

Re: [HACKERS] Custom compression methods

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: 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: 2021-02-11T14:47:02Z
Lists: pgsql-hackers 
On Thu, Feb 11, 2021 at 7:36 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> W.R.T the attached patch, In HeapTupleHeaderGetDatum, we don't even
> attempt to detoast if there is no external field in the tuple, in POC
> I have got rid of that check, but I think we might need to do better.
> Maybe we can add a flag in infomask to detect whether the tuple has
> any compressed data or not as we have for detecting the external data
> (HEAP_HASEXTERNAL).

No. This feature isn't close to being important enough to justify
consuming an infomask bit.

I don't really see why we need it anyway. If array construction
already categorically detoasts, why can't we do the same thing here?
Would it really cost that much? In what case? Having compressed values
in a record we're going to store on disk actually seems like a pretty
dumb idea. We might end up trying to recompress something parts of
which have already been compressed.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

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.