Horton

Re: Add LZ4 compression in pg_dump

gkokolatos@pm.me

View thread View on postgr.es
From: gkokolatos@pm.me
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, Michael Paquier <michael@paquier.xyz>, Justin Pryzby <pryzby@telsasoft.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Rachel Heaton <rachelmheaton@gmail.com>
Date: 2023-03-11T10:50:06Z
Lists: pgsql-hackers

Attachments

------- Original Message -------
On Saturday, March 11th, 2023 at 7:00 AM, Alexander Lakhin <exclusion@gmail.com> wrote:

> Hello,
> 23.02.2023 23:24, Tomas Vondra wrote:
> 
> > On 2/23/23 16:26, Tomas Vondra wrote:
> > 
> > > Thanks for v30 with the updated commit messages. I've pushed 0001 after
> > > fixing a comment typo and removing (I think) an unnecessary change in an
> > > error message.
> > > 
> > > I'll give the buildfarm a bit of time before pushing 0002 and 0003.
> > 
> > I've now pushed 0002 and 0003, after minor tweaks (a couple typos etc.),
> > and marked the CF entry as committed. Thanks for the patch!
> > 
> > I wonder how difficult would it be to add the zstd compression, so that
> > we don't have the annoying "unsupported" cases.
> 
> 
> With the patch 0003 committed, a single warning -Wtype-limits appeared in the
> master branch:
> $ CPPFLAGS="-Og -Wtype-limits" ./configure --with-lz4 -q && make -s -j8
> compress_lz4.c: In function ‘LZ4File_gets’:
> compress_lz4.c:492:19: warning: comparison of unsigned expression in ‘< 0’ is
> always false [-Wtype-limits]
> 492 | if (dsize < 0)
> |

Thank you Alexander. Please find attached an attempt to address it.

> (I wonder, is it accidental that there no other places that triggers
> the warning, or some buildfarm animals had this check enabled before?)

I can not answer about the buildfarms. Do you think that adding an explicit
check for this warning in meson would help? I am a bit uncertain as I think
that type-limits are included in extra.

@@ -1748,6 +1748,7 @@ common_warning_flags = [
   '-Wshadow=compatible-local',
   # This was included in -Wall/-Wformat in older GCC versions
   '-Wformat-security',
+  '-Wtype-limits',
 ]

> 
> It is not a false positive as can be proved by the 002_pg_dump.pl modified as
> follows:
> - program => $ENV{'LZ4'},
> 
> + program => 'mv',
> 
> args => [
> 
> - '-z', '-f', '--rm',
> "$tempdir/compression_lz4_dir/blobs.toc",
> "$tempdir/compression_lz4_dir/blobs.toc.lz4",
> ],
> },

Correct, it is not a false positive. The existing testing framework provides
limited support for exercising error branches. Especially so when those are
dependent on generated output. 

> A diagnostic logging added shows:
> LZ4File_gets() after LZ4File_read_internal; dsize: 18446744073709551615
> 
> and pg_restore fails with:
> error: invalid line in large object TOC file
> ".../src/bin/pg_dump/tmp_check/tmp_test_22ri/compression_lz4_dir/blobs.toc": "????"

It is a good thing that the restore fails with bad input. Yet it should
have failed earlier. The attached makes certain it does fail earlier. 

Cheers,
//Georgios

> 
> Best regards,
> Alexander

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,