Horton

Re: refactoring basebackup.c

Jeevan Ladhe <jeevan.ladhe@enterprisedb.com>

View thread
From: Jeevan Ladhe <jeevan.ladhe@enterprisedb.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Mark Dilger <mark.dilger@enterprisedb.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, tushar <tushar.ahuja@enterprisedb.com>
Date: 2021-10-20T12:48:55Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Document BaseBackupSync and BaseBackupWrite wait events.

  2. Support long distance matching for zstd compression

  3. Fix possible NULL-pointer-deference in backup_compression.c.

  4. Allow parallel zstd compression when taking a base backup.

  5. Make PostgreSQL::Test::Cluster::run_log() return a useful value.

  6. Fix a few goofs in new backup compression code.

  7. Replace BASE_BACKUP COMPRESSION_LEVEL option with COMPRESSION_DETAIL.

  8. Add 'basebackup_to_shell' contrib module.

  9. Allow extensions to add new backup targets.

  10. Change HAVE_LIBLZ4 and HAVE_LIBZSTD tests to USE_LZ4 and USE_ZSTD.

  11. pg_basebackup: Clean up some bogus file extension tests.

  12. pg_basebackup: Avoid unclean failure with server-compression and -D -.

  13. Fix LZ4 tests for remaining buffer space.

  14. Add support for zstd base backup compression.

  15. pg_basebackup: Allow client-side LZ4 (de)compression.

  16. Add suport for server-side LZ4 base backup compression.

  17. Add min() and max() aggregates for xid8.

  18. Remove superfluous variable.

  19. pg_basebackup: Cleaner handling when compression is multiply specified.

  20. Allow server-side compression to be used with -Fp.

  21. pg_basebackup: Fix a couple of recently-introduced bugs.

  22. Tidy up a few cosmetic issues related to pg_basebackup.

  23. Server-side gzip compression.

  24. Unbreak pg_basebackup/t/010_pg_basebackup.pl on msys

  25. Suppress variable-set-but-not-used warning from clang 13.

  26. Extend the options of pg_basebackup to control compression

  27. Support base backup targets.

  28. Modify pg_basebackup to use a new COPY subprotocol for base backups.

  29. Document that tar archives are now properly terminated.

  30. Fix thinko in bbsink_throttle_manifest_contents.

  31. Have the server properly terminate tar archives.

  32. Minimal fix for unterminated tar archive problem.

  33. Introduce 'bbstreamer' abstraction to modularize pg_basebackup.

  34. Introduce 'bbsink' abstraction to modularize base backup code.

  35. Refactor basebackup.c's _tarWriteDir() function.

  36. Flexible options for CREATE_REPLICATION_SLOT.

  37. Flexible options for BASE_BACKUP.

Attachments

Hi Robert,

I mean #define CHUNK_SIZE is still in the patch.
>

Oops, removed now.


> > > With just that change, you can set
> > > next_buf_len = LZ4F_HEADER_SIZE_MAX + mysink->output_buffer_bound --
> > > but that's also more than you need. You can instead do next_buf_len =
> > > Min(LZ4F_HEADER_SIZE_MAX, mysink->output_buffer_bound). Now, you're
> > > probably thinking that won't work, because bbsink_lz4_begin_archive()
> > > could fill up the buffer partway, and then the first call to
> > > bbsink_lz4_archive_contents() could overrun it. But that problem can
> > > be solved by reversing the order of operations in
> > > bbsink_lz4_archive_contents(): before you call LZ4F_compressUpdate(),
> > > test whether you need to empty the buffer first, and if so, do it.
> >
> > I am still not able to get - how can we survive with a mere
> > size of Min(LZ4F_HEADER_SIZE_MAX, mysink->output_buffer_bound).
> > LZ4F_HEADER_SIZE_MAX is defined as 19 in lz4 library. With this
> > proposal, it is almost guaranteed that the next buffer length will
> > be always set to 19, which will result in failure of a call to
> > LZ4F_compressUpdate() with the error LZ4F_ERROR_dstMaxSize_tooSmall,
> > even if we had called bbsink_archive_contents() before.
>
> Sorry, should have been Max(), not Min().
>

Ahh ok.
I looked into the code of LZ4F_compressBound() and the header size is
already included in the calculations, so when we compare
LZ4F_HEADER_SIZE_MAX and mysink->output_buffer_bound, the latter
will be always greater, and hence sufficient length for the output buffer. I
made this change in the attached patch, and also cleared the buffer by
calling bbsink_archive_contents() before calling LZ4_compressUpdate().
Similarly cleared the buffer before calling LZ4F_compressEnd().

> You mean the way gzip allows us to use our own alloc and free functions
> > by means of providing the function pointers for them. Unfortunately,
> > no, LZ4 does not have that kind of provision. Maybe that makes a
> > good proposal for LZ4 library ;-).
> > I cannot think of another solution to it right away.
>
> OK. Will give it some thought.


I have started a thread[1] on LZ4 community for this, but so far no
reply on that.

Regards,
Jeevan Ladhe

[1]
https://groups.google.com/g/lz4c/c/WnJkKwBWlcM/m/zszrla2mBQAJ?utm_medium=email&utm_source=footer