Horton

Re: Add LZ4 compression in pg_dump

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: gkokolatos@pm.me, Rachel Heaton <rachelmheaton@gmail.com>, Greg Stark <stark@mit.edu>, pgsql-hackers@lists.postgresql.org
Date: 2022-03-29T07:27:32Z
Lists: pgsql-hackers 
On Sat, Mar 26, 2022 at 01:14:41AM -0500, Justin Pryzby wrote:
> See 0001 and the manpage.
> 
> +               'pg_dump: compression is not supported by tar archive format');
> 
> When I submitted a patch to support zstd, I spent awhile trying to make
> compression work with tar, but it's a significant effort and better done
> separately.

Wow.  This stuff is old enough to vote (c3e18804), dead since its
introduction.  There is indeed an argument for removing that, it is
not good to keep around that that has never been stressed and/or
used.  Upon review, the cleanup done looks correct, as we have never
been able to generate .dat.gz files in for a dump in the tar format.

+   command_fails_like(
+       [ 'pg_dump', '--compress', '1', '--format', 'tar' ],
This addition depending on HAVE_LIBZ is a good thing as a reminder of
any work that could be done in 0002.  Now that's waiting for 20 years
so I would not hold my breath on this support.  I think that this
could be just applied first, with 0002 on top of it, as a first
improvement.

+       compress_cmd => [
+           $ENV{'GZIP_PROGRAM'},
Patch 0001 is missing and update of pg_dump's Makefile to pass down
this environment variable to the test scripts, no?

+       compress_cmd => [
+           $ENV{'GZIP_PROGRAM'},
+           '-f',
[...]
+           $ENV{'GZIP_PROGRAM'},
+           '-k', '-d',
-f and -d are available everywhere I looked at, but is -k/--keep a
portable choice with a gzip command?  I don't see this option in
OpenBSD, for one.  So this test is going to cause problems on those
buildfarm machines, at least.  Couldn't this part be replaced by a
simple --test to check that what has been compressed is in correct
shape?  We know that this works, based on our recent experiences with
the other tests.
--
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,