Horton

Re: Add LZ4 compression in pg_dump

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: gkokolatos@pm.me
Cc: Michael Paquier <michael@paquier.xyz>, Tomas Vondra <tomas.vondra@enterprisedb.com>, pgsql-hackers@lists.postgresql.org, Rachel Heaton <rachelmheaton@gmail.com>
Date: 2023-01-26T18:22:45Z
Lists: pgsql-hackers 
On Wed, Jan 25, 2023 at 07:57:18PM +0000, gkokolatos@pm.me wrote:
> On Wednesday, January 25th, 2023 at 7:00 PM, Justin Pryzby <pryzby@telsasoft.com> wrote:
> > While looking at this, I realized that commit 5e73a6048 introduced a
> > regression:
> > 
> > @@ -3740,19 +3762,24 @@ ReadHead(ArchiveHandle *AH)
> > 
> > - if (AH->compression != 0)
> > 
> > - pg_log_warning("archive is compressed, but this installation does not support compression -- no data will be available");
> > + if (AH->compression_spec.algorithm == PG_COMPRESSION_GZIP)
> > 
> > + pg_fatal("archive is compressed, but this installation does not support compression");
> > 
> > Before, it was possible to restore non-data chunks of a dump file, even
> > if the current build didn't support its compression. But that's now
> > impossible - and it makes the code we're discussing in RestoreArchive()
> > unreachable.

On Thu, Jan 26, 2023 at 08:53:28PM +0900, Michael Paquier wrote:
> On Thu, Jan 26, 2023 at 11:24:47AM +0000, gkokolatos@pm.me wrote:
> > I gave this a little bit of thought. I think that ReadHead should not
> > emit a warning, or at least not this warning as it is slightly misleading.
> > It implies that it will automatically turn off data restoration, which is
> > false. Further ahead, the code will fail with a conflicting error message
> > stating that the compression is not available.
> > 
> > Instead, it would be cleaner both for the user and the maintainer to
> > move the check in RestoreArchive and make it the sole responsible for
> > this logic.
> 
> -    pg_fatal("cannot restore from compressed archive (compression not supported in this installation)");
> +    pg_fatal("cannot restore data from compressed archive (compression not supported in this installation)");
> Hmm.  I don't mind changing this part as you suggest.
> 
> -#ifndef HAVE_LIBZ
> -       if (AH->compression_spec.algorithm == PG_COMPRESSION_GZIP)
> -               pg_fatal("archive is compressed, but this installation does not support compression");
> -#endif
> However I think that we'd better keep the warning, as it can offer a
> hint when using pg_restore -l not built with compression support if
> looking at a dump that has been compressed.

Yeah.  But the original log_warning text was better, and should be
restored:

-       if (AH->compression != 0)
-               pg_log_warning("archive is compressed, but this installation does not support compression -- no data will be available");

That commit also added this to pg-dump.c:

+               case PG_COMPRESSION_ZSTD:
+                       pg_fatal("compression with %s is not yet supported", "ZSTD");
+                       break;
+               case PG_COMPRESSION_LZ4:
+                       pg_fatal("compression with %s is not yet supported", "LZ4");
+                       break;

In 002, that could be simplified by re-using the supports_compression()
function.  (And maybe the same in WriteDataToArchive()?)

-- 
Justin

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,