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>, Rachel Heaton <rachelmheaton@gmail.com>, Greg Stark <stark@mit.edu>, pgsql-hackers@lists.postgresql.org
Date: 2022-03-30T05:54:34Z
Lists: pgsql-hackers 
On Tue, Mar 29, 2022 at 09:46:27AM +0000, gkokolatos@pm.me wrote:
> 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:
>> 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.

Makes sense to me.

>> + 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.

I have applied the test for --compress and --format=tar, separating it
from the rest.

While moving on with 0002, I have noticed the following in
_StartBlob():
    if (AH->compression != 0)
        sfx = ".gz";
    else
        sfx = "";
	
Shouldn't this bit also be simplified, adding a fatal() like the other
code paths, for safety?

>> + 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.

Ahh, I see, thanks.  I would add a comment about that in the area of
compression_gzip_plain_format.

+   my $supports_compression = check_pg_config("#define HAVE_LIBZ 1");

This part could be moved within the if block a couple of lines down.

+   my $compress_program = $ENV{GZIP_PROGRAM};

It seems to me that it is enough to rely on {compress_cmd}, hence
there should be no need for $compress_program, no?

It seems to me that we should have a description for compress_cmd at
the top of 002_pg_dump.pl (close to "Definition of the pg_dump runs to
make").  There is an order dependency with restore_cmd.

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

Okay.
--
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,