Horton

Re: [HACKERS] logical decoding of two-phase transactions

vignesh C <vignesh21@gmail.com>

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From: vignesh C <vignesh21@gmail.com>
To: Peter Smith <smithpb2250@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, Ajin Cherian <itsajin@gmail.com>, Greg Nancarrow <gregn4422@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2021-07-16T06:08:24Z
Lists: pgsql-hackers 
On Wed, Jul 14, 2021 at 2:03 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> On Wed, Jul 14, 2021 at 4:23 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Mon, Jul 12, 2021 at 9:14 AM Peter Smith <smithpb2250@gmail.com> wrote:
> > >
> > > On Sun, Jul 11, 2021 at 8:20 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > >
> > > > On Fri, Jul 9, 2021 at 4:43 AM Peter Smith <smithpb2250@gmail.com> wrote:
> > > > >
> > > > > > The patch looks good to me, I don't have any comments.
> > > > >
> > > > > I tried the v95-0001 patch.
> > > > >
> > > > > - The patch applied cleanly and all build / testing was OK.
> > > > > - The documentation also builds OK.
> > > > > - I checked all v95-0001 / v93-0001 differences and found no problems.
> > > > > - Furthermore, I noted that v95-0001 patch is passing the cfbot [1].
> > > > >
> > > > > So this patch LGTM.
> > > > >
> > > >
> > > > Thanks, I took another pass over it and made a few changes in docs and
> > > > comments. I am planning to push this next week sometime (by 14th July)
> > > > unless there are more comments from you or someone else. Just to
> > > > summarize, this patch will add support for prepared transactions to
> > > > built-in logical replication. To add support for streaming
> > > > transactions at prepare time into the
> > > > built-in logical replication, we need to do the following things: (a)
> > > > Modify the output plugin (pgoutput) to implement the new two-phase API
> > > > callbacks, by leveraging the extended replication protocol. (b) Modify
> > > > the replication apply worker, to properly handle two-phase
> > > > transactions by replaying them on prepare. (c) Add a new SUBSCRIPTION
> > > > option "two_phase" to allow users to enable
> > > > two-phase transactions. We enable the two_phase once the initial data
> > > > sync is over. Refer to comments atop worker.c in the patch and commit
> > > > message to see further details about this patch. After this patch,
> > > > there is a follow-up patch to allow streaming and two-phase options
> > > > together which I feel needs some more review and can be committed
> > > > separately.
> > > >
> > >
> > > FYI - I repeated the same verification of the v96-0001 patch as I did
> > > previously for v95-0001
> > >
> > > - The v96 patch applied cleanly and all build / testing was OK.
> > > - The documentation also builds OK.
> > > - I checked the v95-0001 / v96-0001 differences and found no problems.
> > > - Furthermore, I noted that v96-0001 patch is passing the cfbot.
> > >
> > > LGTM.
> > >
> >
> > Pushed.
> >
> > Feel free to submit the remaining patches after rebase. Is it possible
> > to post patches related to skipping empty transactions in the other
> > thread [1] where that topic is being discussed?
> >
> > [1] - https://www.postgresql.org/message-id/CAMkU%3D1yohp9-dv48FLoSPrMqYEyyS5ZWkaZGD41RJr10xiNo_Q%40mail.gmail.com
> >
>
>
> Please find attached the latest patch set v97*
>
> * Rebased v94* to HEAD @ today.

Thanks for the updated patch, the patch applies cleanly and test passes:
I had couple of comments:
1) Should we include "stream_prepare_cb" here  in
logicaldecoding-streaming section of logicaldecoding.sgml
documentation:
To reduce the apply lag caused by large transactions, an output plugin
may provide additional callback to support incremental streaming of
in-progress transactions. There are multiple required streaming
callbacks (stream_start_cb, stream_stop_cb, stream_abort_cb,
stream_commit_cb and stream_change_cb) and two optional callbacks
(stream_message_cb and stream_truncate_cb).

2) Should we add an example for stream_prepare_cb here  in
logicaldecoding-streaming section of logicaldecoding.sgml
documentation:
One example sequence of streaming callback calls for one transaction
may look like this:

stream_start_cb(...);   <-- start of first block of changes
  stream_change_cb(...);
  stream_change_cb(...);
  stream_message_cb(...);
  stream_change_cb(...);
  ...
  stream_change_cb(...);
stream_stop_cb(...);    <-- end of first block of changes

stream_start_cb(...);   <-- start of second block of changes
  stream_change_cb(...);
  stream_change_cb(...);
  stream_change_cb(...);
  ...
  stream_message_cb(...);
  stream_change_cb(...);
stream_stop_cb(...);    <-- end of second block of changes

stream_commit_cb(...);  <-- commit of the streamed transaction

Regards,
Vignesh

Commits

  1. Add prepare API support for streaming transactions in logical replication.

  2. Doc: minor improvements for logical replication protocol documentation.

  3. Fix test failure in 021_twophase.pl.

  4. Refactor to make common functions in proto.c and worker.c.

  5. Unify PostgresNode's new() and get_new_node() methods

  6. Fix potential buffer overruns in proto.c.

  7. Add support for prepared transactions to built-in logical replication.

  8. Refactor function parse_subscription_options.

  9. Allow enabling two-phase option via replication protocol.

  10. Don't use Asserts to check for violations of replication protocol.

  11. Improve psql tab completion for options of subcriptions and publications

  12. Rearrange logrep worker's snapshot handling some more.

  13. doc: Update information of new messages for logical replication.

  14. ALTER SUBSCRIPTION ... ADD/DROP PUBLICATION

  15. Allow pgoutput to send logical decoding messages.

  16. Refactor function parse_output_parameters.

  17. Avoid repeated decoding of prepared transactions after a restart.

  18. Fix an oversight in ReorderBufferFinishPrepared.

  19. Allow multiple xacts during table sync in logical replication.

  20. Fix replication of in-progress transactions in tablesync worker.

  21. Fix 'skip-empty-xacts' option in test_decoding for streaming mode.

  22. Use Enum for top level logical replication message types.

  23. Add support for streaming to built-in logical replication.

  24. Fix the logical streaming test.

  25. Implement streaming mode in ReorderBuffer.

  26. Extend the logical decoding output plugin API with stream methods.

  27. Store 2PC GID in commit/abort WAL recs for logical decoding