Horton

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

Ajin Cherian <itsajin@gmail.com>

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From: Ajin Cherian <itsajin@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-09-21T10:14:47Z
Lists: pgsql-hackers 
On Sun, Sep 20, 2020 at 3:31 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:

> + /*
> + * If it's ROLLBACK PREPARED then handle it via callbacks.
> + */
> + if (TransactionIdIsValid(xid) &&
> + !SnapBuildXactNeedsSkip(ctx->snapshot_builder, buf->origptr) &&
> + parsed->dbId == ctx->slot->data.database &&
> + !FilterByOrigin(ctx, origin_id) &&
> + ReorderBufferTxnIsPrepared(ctx->reorder, xid, parsed->twophase_gid))
> + {
> + ReorderBufferFinishPrepared(ctx->reorder, xid, buf->origptr, buf->endptr,
> + commit_time, origin_id, origin_lsn,
> + parsed->twophase_gid, false);
> + return;
> + }
>
>
> I think we have already checked !SnapBuildXactNeedsSkip, parsed->dbId
> == ctx->slot->data.database and !FilterByOrigin in DecodePrepare
> so if those are not true then we wouldn't have prepared this
> transaction i.e. ReorderBufferTxnIsPrepared will be false so why do we
> need
> to recheck this conditions.

We could enter DecodeAbort even without a prepare, as the code is
common for both XLOG_XACT_ABORT and XLOG_XACT_ABORT_PREPARED. So, the
conditions !SnapBuildXactNeedsSkip, parsed->dbId
> == ctx->slot->data.database and !FilterByOrigin could be true but the transaction is not prepared, then we dont need to do a ReorderBufferFinishPrepared (with commit flag false) but called ReorderBufferAbort. But I think there is a problem, if those conditions are in fact false, then we should return without trying to Abort using ReorderBufferAbort, what do you think?

I agree with all your other comments.

regards,
Ajin
Fujitsu Australia

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