Horton

Re: Add LZ4 compression in pg_dump

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: gkokolatos@pm.me
Cc: Justin Pryzby <pryzby@telsasoft.com>, Alexander Lakhin <exclusion@gmail.com>, shiy.fnst@fujitsu.com, Michael Paquier <michael@paquier.xyz>, pgsql-hackers@lists.postgresql.org, Rachel Heaton <rachelmheaton@gmail.com>
Date: 2023-03-31T23:34:16Z
Lists: pgsql-hackers 
On 3/31/23 11:19, gkokolatos@pm.me wrote:
> 
>> ...
>>
>>
>> I think the patch is fine, but I'm wondering if the renames shouldn't go
>> a bit further. It removes references to LZ4File struct, but there's a
>> bunch of functions with LZ4File_ prefix. Why not to simply use LZ4_
>> prefix? We don't have GzipFile either.
>>
>> Sure, it might be a bit confusing because lz4.h uses LZ4_ prefix, but
>> then we probably should not define LZ4_compressor_init ...
> 
> This is a good point. The initial thought was that since lz4.h is now
> removed, such ambiguity will not be present. In v2 of the patch the
> function is renamed to `LZ4State_compression_init` since this name
> describes better its purpose. It initializes the LZ4State for
> compression.
> 
> As for the LZ4File_ prefix, I have no objections. Please find the
> prefix changed to LZ4Stream_. For the record, the word 'File' is not
> unique to the lz4 implementation. The common data structure used by
> the API in compress_io.h:
> 
>    typedef struct CompressFileHandle CompressFileHandle; 
> 
> The public functions for this API are named:
> 
>   InitCompressFileHandle
>   InitDiscoverCompressFileHandle
>   EndCompressFileHandle
> 
> And within InitCompressFileHandle the pattern is:
> 
>     if (compression_spec.algorithm == PG_COMPRESSION_NONE)
>         InitCompressFileHandleNone(CFH, compression_spec);
>     else if (compression_spec.algorithm == PG_COMPRESSION_GZIP)
>         InitCompressFileHandleGzip(CFH, compression_spec);
>     else if (compression_spec.algorithm == PG_COMPRESSION_LZ4)
>         InitCompressFileHandleLZ4(CFH, compression_spec);
> 
> It was felt that a prefix was required due to the inclusion 'lz4.h'
> header where naming functions as 'LZ4_' would be wrong. The prefix
> 'LZ4File_' seemed to be in line with the naming of the rest of
> the relevant functions and structures. Other compressions, gzip and
> none, did not face the same issue.
> 
> To conclude, I think that having a prefix is slightly preferred
> over not having one. Since the prefix `LZ4File_` is not desired,
> I propose `LZ4Stream_` in v2.
> 
> I will not object to dismissing the argument and drop `File` from
> the prefix, if so requested.
> 

Thanks.

I think the LZ4Stream prefix is reasonable, so let's roll with that. I
cleaned up the patch a little bit (mostly comment tweaks, etc.), updated
the commit message and pushed it.

The main tweak I did is renaming all the LZ4State variables from "fs" to
state. The old name referred to the now abandoned "file state", but
after the rename to LZ4State that seems confusing. Some of the places
already used "state"and it's easier to know "state" is always LZ4State,
so let's keep it consistent.

regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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,