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: Tomas Vondra <tomas.vondra@enterprisedb.com>, shiy.fnst@fujitsu.com, Michael Paquier <michael@paquier.xyz>, pgsql-hackers@lists.postgresql.org, Rachel Heaton <rachelmheaton@gmail.com>
Date: 2023-03-01T17:08:17Z
Lists: pgsql-hackers 
On Wed, Mar 01, 2023 at 01:39:14PM +0000, gkokolatos@pm.me wrote:
> On Wednesday, March 1st, 2023 at 12:58 AM, Justin Pryzby <pryzby@telsasoft.com> wrote:
> 
> > The current function order avoids 3 lines of declarations, but it's
> > obviously pretty useful to be able to run that diff command. I already
> > argued for not calling the functions "Gzip" on the grounds that the name
> > was inaccurate.
> 
> I have no idea why we are back on the naming issue. I stand by the name
> because in my humble opinion helps the code reader. There is a certain
> uniformity when the compression_spec.algorithm and the compressor
> functions match as the following code sample shows.

I mentioned that it's because this allows usefully running "diff"
against the previous commits.

>     if (compression_spec.algorithm == PG_COMPRESSION_NONE)         
>         InitCompressorNone(cs, compression_spec);
>     else if (compression_spec.algorithm == PG_COMPRESSION_GZIP)
>         InitCompressorGzip(cs, compression_spec);
>     else if (compression_spec.algorithm == PG_COMPRESSION_LZ4)
>         InitCompressorLZ4(cs, compression_spec);        
>                                                  
> When the reader wants to see what happens when the PG_COMPRESSION_XXX
> is set, has to simply search for the XXX part. I think that this is
> justification enough for the use of the names.

You're right about that.

But (with the exception of InitCompressorGzip), I'm referring to the
naming of internal functions, static to gzip.c, so renaming can't be
said to cause a loss of clarity.

> > I'd want to create an empty large object in src/test/sql/largeobject.sql
> > to exercise this tested during pgupgrade. But unfortunately that
> > doesn't use -Fc, so this isn't hit. Empty input is an important enough
> > test case to justify a tap test, if there's no better way.
> 
> Please find in the attached a test case that exercises this codepath.

Thanks for writing it.

This patch could be an opportunity to improve the "diff" output, without
renaming anything.

The old order of functions was:
-InitCompressorZlib
-EndCompressorZlib
-DeflateCompressorZlib
-WriteDataToArchiveZlib
-ReadDataFromArchiveZlib

If you put DeflateCompressorEnd immediately after DeflateCompressorInit,
diff works nicely.  You'll have to add at least one declaration, which
seems very worth it.

-- 
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,