Horton

Re: refactoring basebackup.c

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Jeevan Ladhe <jeevan.ladhe@enterprisedb.com>
Cc: tushar <tushar.ahuja@enterprisedb.com>, Dmitry Dolgov <9erthalion6@gmail.com>, Mark Dilger <mark.dilger@enterprisedb.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2022-01-18T21:27:18Z
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.

On Tue, Jan 18, 2022 at 9:43 AM Jeevan Ladhe
<jeevan.ladhe@enterprisedb.com> wrote:
> The patch surely needs some grooming, but I am expecting some initial
> review, specially in the area where we are trying to close the zstd stream
> in bbsink_zstd_end_archive(). We need to tell the zstd library to end the
> compression by calling ZSTD_compressStream2() thereby sending a
> ZSTD_e_end flag. But, this also needs some input string, which per
> example[1] line # 686, I have taken as an empty ZSTD_inBuffer.

As far as I can see, this is correct. I found
https://zstd.docsforge.com/dev/api-documentation/#streaming-compression-howto
which seems to endorse what you've done here.

One (minor) thing that I notice is that, the way you've written the
loop in bbsink_zstd_end_archive(), I think it will typically call
bbsink_archive_contents() twice. It will flush whatever is already
present in the next sink's buffer as a result of the previous calls to
bbsink_zstd_archive_contents(), and then it will call
ZSTD_compressStream2() which will partially refill the buffer you just
emptied, and then there will be nothing left in the internal buffer,
so it will call bbsink_archive_contents() again. But ... the initial
flush may not have been necessary. It could be that there was enough
space already in the output buffer for the ZSTD_compressStream2() call
to succeed without a prior flush. So maybe:

do
{
    yet_to_flush = ZSTD_compressStream2(..., ZSTD_e_end);
    check ZSTD_isError here;
    if (mysink->zstd_outBuf.pos > 0)
        bbsink_archive_contents();
} while (yet_to_flush > 0);

I believe this might be very slightly more efficient.

-- 
Robert Haas
EDB: http://www.enterprisedb.com