Horton

Re: Add LZ4 compression in pg_dump

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: gkokolatos@pm.me, pgsql-hackers@lists.postgresql.org, Rachel Heaton <rachelmheaton@gmail.com>
Date: 2023-01-27T03:56:32Z
Lists: pgsql-hackers 
On Mon, Jan 16, 2023 at 11:54:46AM +0900, Michael Paquier wrote:
> On Sun, Jan 15, 2023 at 07:56:25PM -0600, Justin Pryzby wrote:
> > On Mon, Jan 16, 2023 at 10:28:50AM +0900, Michael Paquier wrote:
> >> The functions changed by 0001 are cfopen[_write](),
> >> AllocateCompressor() and ReadDataFromArchive().  Why is it a good idea
> >> to change these interfaces which basically exist to handle inputs?
> > 
> > I changed to pass pg_compress_specification as a pointer, since that's
> > the usual convention for structs, as followed by the existing uses of
> > pg_compress_specification.
> 
> Okay, but what do we gain here?  It seems to me that this introduces
> the risk that a careless change in one of the internal routines if
> they change slight;ly compress_spec, hence impacting any of their
> callers?  Or is that fixing an actual bug (except if I am missing your
> point, that does not seem to be the case)?  

To circle back to this: I was not saying there's any bug.  The proposed
change was only to follow normal and existing normal conventions for
passing structs.  It could also be a pointer to const.  It's fine with
me if you say that it's intentional how it's written already.

> >> Is there some benefit in changing compression_spec within the
> >> internals of these routines before going back one layer down to their
> >> callers?  Changing the compression_spec on-the-fly in these internal
> >> paths could be risky, actually, no?
> > 
> > I think what you're saying is that if the spec is passed as a pointer,
> > then the called functions shouldn't set spec->algorithm=something.
> 
> Yes.  HEAD makes sure of that, 0001 would not prevent that.  So I am a
> bit confused in seeing how this is a benefit.

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,