Horton

Re: Add LZ4 compression in pg_dump

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: gkokolatos@pm.me
Cc: Justin Pryzby <pryzby@telsasoft.com>, pgsql-hackers@lists.postgresql.org, Rachel Heaton <rachelmheaton@gmail.com>
Date: 2022-12-02T01:56:26Z
Lists: pgsql-hackers 
On Thu, Dec 01, 2022 at 02:58:35PM +0000, gkokolatos@pm.me wrote:
> Nuking the warning from orbit and changing the behaviour around disabling
> the requested compression when the libraries are not present, should not
> mean that we need to change the behaviour of default values for different
> formats. Please find v13 attached which reinstates it.

Gah, thanks!  And this default behavior is documented as dependent on
the compilation as well.

> Which in itself it got me looking and wondering why the tests succeeded.
> The only existing test covering that path is `defaults_dir_format` in
> `002_pg_dump.pl`. However as the test is currently written it does not
> check whether the output was compressed. The restore command would succeed
> in either case. A simple `gzip -t -r` against the directory will not
> suffice to test it, because there exist files which are never compressed
> in this format (.toc). A little bit more involved test case would need
> to be written, yet before I embark to this journey, I would like to know
> if you would agree to reinstate the defaults for those formats.

On top of my mind, I briefly recall that -r is not that portable.  And
the toc format makes the files generated non-deterministic as these
use OIDs..

[.. thinks ..]

We are going to need a new thing here, as compress_cmd cannot be
directly used.  What if we used only an array of glob()-able elements?
Let's say "expected_contents" that could include a "dir_path/*.gz"
conditional on $supports_gzip?  glob() can only be calculated when the
test is run as the file names cannot be known beforehand :/

>> As per the patch, it is true that we do not need to bump the format of
>> the dump archives, as we can still store only the compression level
>> and guess the method from it. I have added some notes about that in
>> ReadHead and WriteHead to not forget.
> 
> Agreed. A minor suggestion if you may.
> 
>  #ifndef HAVE_LIBZ
> -       if (AH->compression != 0)
> +       if (AH->compression_spec.algorithm == PG_COMPRESSION_GZIP)
>                 pg_log_warning("archive is compressed, but this installation does not support compression -- no data will be available");
>  #endif
> 
> It would seem a more consistent to error out in this case. We do error
> in all other cases where the compression is not available.

Makes sense.

I have gone through the patch again, and applied it.  Thanks!
--
Michael

Commits

  1. Advance input pointer when LZ4 compressing data

  2. Null-terminate the output buffer of LZ4Stream_gets

  3. Rework code defining default compression for dir/custom formats in pg_dump

  4. pg_dump: Use only LZ4 frame format for compression

  5. Minor comment improvements for compress_lz4

  6. Unify buffer sizes in pg_dump compression API

  7. Improve type handling in pg_dump's compress file API

  8. Improve wording in pg_dump compression docs

  9. Fix condition in pg_dump TAP test

  10. Add LZ4 compression to pg_dump

  11. Introduce a generic pg_dump compression API

  12. Prepare pg_dump internals for additional compression methods

  13. Fix behavior with pg_restore -l and compressed dumps

  14. Add 250c8ee07ed to git-blame-ignore-revs

  15. Provide test coverage in pg_dump for default behaviors with compression

  16. Switch pg_dump to use compression specifications

  17. Refactor code parsing compression option values (-Z/--compress)

  18. meson: Add some missing env settings for tests of pg_dump and pg_verifybackup

  19. Extend TAP tests of pg_dump to test for compression with gzip

  20. Clean up some dead code in pg_dump with tar format and gzip compression

  21. Add TAP test in pg_dump with --format=tar and --compress

  22. Replace BASE_BACKUP COMPRESSION_LEVEL option with COMPRESSION_DETAIL.

  23. Refactor the pg_dump zlib code from pg_backup_custom.c to a separate file,