Horton

Re: [HACKERS] Custom compression methods

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, David Steele <david@pgmasters.net>, Ildus Kurbangaliev <i.kurbangaliev@gmail.com>, Dmitry Dolgov <9erthalion6@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-22T20:33:55Z
Lists: pgsql-hackers

Attachments

On Mon, Mar 22, 2021 at 1:58 PM Justin Pryzby <pryzby@telsasoft.com> wrote:
> guc.c should not longer define this as extern:
> default_toast_compression_options

Fixed.

> I think you should comment that default_toast_compression is an int as far as
> guc.c is concerned, but storing one of the char value of TOAST_*_COMPRESSION

Done.

> Shouldn't varlena.c pg_column_compression() call GetCompressionMethodName () ?
> I guess it should already have done that.

It has a 0-3 integer, not a char value.

> Maybe pg_dump.c can't use those constants, though (?)

Hmm, toast_compression.h might actually be safe for frontend code now,
or if necessary we could add #ifdef FRONTEND stanzas to make it so. I
don't know if that is really this patch's job, but I guess it could
be.

A couple of other things:

- Upon further reflection, I think the NO_LZ4_SUPPORT() message is
kinda not great. I'm thinking we should change it to say "LZ4 is not
supported by this build" instead of "unsupported LZ4 compression
method" and drop the hint and detail. That seems more like how we've
handled other such cases.

- It is not very nice that the three possible values of attcompression
are TOAST_PGLZ_COMPRESSION, TOAST_LZ4_COMPRESSION, and
InvalidCompressionMethod. One of those three identifiers looks very
little like the other two, and there's no real good reason for that. I
think we should try to standardize on something, but I'm not sure what
it should be. It would also be nice if these names were more visually
distinct from the related but very different enum values
TOAST_PGLZ_COMPRESSION_ID and TOAST_LZ4_COMPRESSION_ID. Really, as the
comments I added explain, we want to minimize the amount of code that
knows about the 0-3 "ID" values, and use the char values whenever we
can.

-- 
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.