Horton

Re: Add LZ4 compression in pg_dump

gkokolatos@pm.me

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From: gkokolatos@pm.me
To: Michael Paquier <michael@paquier.xyz>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Rachel Heaton <rachelmheaton@gmail.com>, Greg Stark <stark@mit.edu>, pgsql-hackers@lists.postgresql.org
Date: 2022-03-29T09:46:27Z
Lists: pgsql-hackers

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------- Original Message -------

On Tuesday, March 29th, 2022 at 9:27 AM, Michael Paquier <michael@paquier.xyz> wrote:

> 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.

Correct. My driving force behind it was to ease up the cleanup/refactoring
work that follows, by eliminating the callers of the GZ*() macros.

> + 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.

Excellent, thank you.

> + 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?

Agreed. It was not properly moved forward. Fixed.

> + 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.

I would argue that the simple '--test' will not do in this case, as the
TAP tests do need a file named <test>.sql to compare the contents with.
This file is generated either directly by pg_dump itself, or by running
pg_restore on pg_dump's output. In the case of compression pg_dump will
generate a <test>.sql.<compression program suffix> which can not be
used in the comparison tests. So the intention of this block, is not to
simply test for validity, but to also decompress pg_dump's output for it
to be able to be used.

I updated the patch to simply remove the '-k' flag.

Please find v3 attached. (only 0001 and 0002 are relevant, 0003 and
0004 are only for reference and are currently under active modification).

Cheers,
//Georgios

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,