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>, pgsql-hackers@lists.postgresql.org, Rachel Heaton <rachelmheaton@gmail.com>
Date: 2023-01-14T21:43:09Z
Lists: pgsql-hackers

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On Sun, Jan 08, 2023 at 01:45:25PM -0600, Justin Pryzby wrote:
> On Thu, Dec 22, 2022 at 11:08:59AM -0600, Justin Pryzby wrote:
> > There's a couple of lz4 bits which shouldn't be present in 002: file
> > extension and comments.

> BTW I noticed that cfdopen() was accidentally committed to compress_io.h
> in master without being defined anywhere.

This was resolved in 69fb29d1a (so now needs to be re-added for this
patch series).

> pg_compress_specification is being passed by value, but I think it
> should be passed as a pointer, as is done everywhere else.

ISTM that was an issue with 5e73a6048, affecting a few public and
private functions.  I wrote a pre-preparatory patch which changes to
pass by reference.

And addressed a handful of other issues I reported as separate fixup
commits.  And changed to use LZ4 by default for CI.

I also rebased my 2 year old patch to support zstd in pg_dump.  I hope
it can finally added for v16.  I'll send it for the next CF if these
patches progress.

One more thing: some comments still refer to the cfopen API, which this
patch removes.

> There were "LZ4" comments and file extension stuff in the preparatory
> commit.  But now it seems like you *removed* them in the LZ4 commit
> (where it actually belongs) rather than *moving* it from the
> prior/parent commit *to* the lz4 commit.  I recommend to run something
> like "git diff @{1}" whenever doing this kind of patch surgery.

TODO

> Maybe other places that check if (compression==PG_COMPRESSION_GZIP)
> should maybe change to say compression!=NONE?
> 
> _PrepParallelRestore() references ".gz", so I think it needs to be
> retrofitted to handle .lz4.  Ideally, that's built into a struct or list
> of file extensions to try.  Maybe compression.h should have a function
> to return the file extension of a given algorithm.  I'm planning to send
> a patch for zstd, and hoping its changes will be minimized by these
> preparatory commits.

TODO

> I think it's confusing to have two functions, one named
> InitCompressLZ4() and InitCompressorLZ4().

TODO

> pg_compress_algorithm is being writen directly into the pg_dump header.
> Currently, I think that's not an externally-visible value (it could be
> renumbered, theoretically even in a minor release).  Maybe there should
> be a "private" enum for encoding the pg_dump header, similar to
> WAL_COMPRESSION_LZ4 vs BKPIMAGE_COMPRESS_LZ4 ?  Or else a comment there
> should warn that the values are encoded in pg_dump, and must never be
> changed.

Michael, WDYT ?

-- 
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,