Horton

Re: Add LZ4 compression in pg_dump

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Paquier <michael@paquier.xyz>
Cc: gkokolatos@pm.me, Justin Pryzby <pryzby@telsasoft.com>, Rachel Heaton <rachelmheaton@gmail.com>, Greg Stark <stark@mit.edu>, pgsql-hackers@lists.postgresql.org
Date: 2025-10-12T17:24:37Z
Lists: pgsql-hackers 
[ blast-from-the-past department ]

Michael Paquier <michael@paquier.xyz> writes:
> At the end I am finishing with the attached.  I also saw an overlap
> with the addition of --jobs for the directory format vs not using the
> option, so I have removed the case where --jobs was not used in the
> directory format.

(This patch became commit 98fe74218.)

I am wondering if you remember why this bit:

+        # Give coverage for manually compressed blob.toc files during
+        # restore.
+        compress_cmd => {
+            program => $ENV{'GZIP_PROGRAM'},
+            args    => [ '-f', "$tempdir/compression_gzip_dir/blobs.toc", ],
+        },

was set up to manually compress blobs.toc but not the main TOC in the
toc.dat file.  It turns out that Gzip_read is broken for the case
of a zero-length read request [1], but we never reach that case
unless toc.dat is compressed.  We don't cover the getc_func member
of the compression stream API, either.

I thought for a bit about proposing that we compress toc.dat but not
blobs.toc, but that loses coverage in another way: the gets_func API
turns out to be used only while reading blobs.toc.  So we need to
compress both files manually if we want full coverage.

I think this change won't lose coverage, because there are other tests
in 002_pg_dump.pl that exercise directory format without extra
compression of anything.

Thoughts?

			regards, tom lane

[1] https://www.postgresql.org/message-id/3686.1760232320%40sss.pgh.pa.us

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,