Horton

Re: [HACKERS] Custom compression methods (mac+lz4.h)

Dilip Kumar <dilipbalaut@gmail.com>

View thread View on postgr.es
From: Dilip Kumar <dilipbalaut@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, 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>, Andrey Borodin <x4mmm@yandex-team.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-22T15:27:59Z
Lists: pgsql-hackers

Attachments

On Mon, Mar 22, 2021 at 8:11 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Dilip Kumar <dilipbalaut@gmail.com> writes:
> > On Mon, Mar 22, 2021 at 5:22 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> Also, after studying the documentation for LZ4_decompress_safe
> >> and LZ4_decompress_safe_partial, I realized that liblz4 is also
> >> counting on the *output* buffer size to not be a lie.  So we
> >> cannot pass it a number larger than the chunk's true decompressed
> >> size.  The attached patch resolves the issue I'm seeing.
>
> > Okay, the fix makes sense.  In fact, IMHO, in general also this fix
> > looks like an optimization, I mean when slicelength >=
> > VARRAWSIZE_4B_C(value), then why do we need to allocate extra memory
> > even in the case of pglz.  So shall we put this check directly in
> > toast_decompress_datum_slice instead of handling it at the lz4 level?
>
> Yeah, I thought about that too, but do we want to assume that
> VARRAWSIZE_4B_C is the correct way to get the decompressed size
> for all compression methods?

Yeah, VARRAWSIZE_4B_C is the macro getting the rawsize of the data
stored in the compressed varlena.

> (If so, I think it would be better style to have a less opaque macro
> name for the purpose.)

Okay, I have added another macro that is less opaque and came up with
this patch.

-- 
Regards,
Dilip Kumar
EnterpriseDB: 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.