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: Ajin Cherian <itsajin@gmail.com>
Cc: Greg Nancarrow <gregn4422@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2021-06-23T05:17:49Z
Lists: pgsql-hackers 
On Wed, Jun 23, 2021 at 9:10 AM Ajin Cherian <itsajin@gmail.com> wrote:
>
> On Tue, Jun 22, 2021 at 3:36 PM Greg Nancarrow <gregn4422@gmail.com> wrote:
>
> > Some minor comments:
> >
> > (1)
> > v88-0002
> >
> > doc/src/sgml/logicaldecoding.sgml
> >
> > "examples shows" is not correct.
> > I think there is only ONE example being referred to.
> >
> > BEFORE:
> > +    The following examples shows how logical decoding is controlled over the
> > AFTER:
> > +    The following example shows how logical decoding is controlled over the
> >
> >
> fixed.
>
> > (2)
> > v88 - 0003
> >
> > doc/src/sgml/ref/create_subscription.sgml
> >
> > (i)
> >
> > BEFORE:
> > +          to the subscriber on the PREPARE TRANSACTION. By default,
> > the transaction
> > +          prepared on publisher is decoded as a normal transaction at commit.
> > AFTER:
> > +          to the subscriber on the PREPARE TRANSACTION. By default,
> > the transaction
> > +          prepared on the publisher is decoded as a normal
> > transaction at commit time.
> >
>
> fixed.
>
> > (ii)
> >
> > src/backend/access/transam/twophase.c
> >
> > The double-bracketing is unnecessary:
> >
> > BEFORE:
> > + if ((gxact->valid && strcmp(gxact->gid, gid) == 0))
> > AFTER:
> > + if (gxact->valid && strcmp(gxact->gid, gid) == 0)
> >
>
> fixed.
>
> > (iii)
> >
> > src/backend/replication/logical/snapbuild.c
> >
> > Need to add some commas to make the following easier to read, and
> > change "needs" to "need":
> >
> > BEFORE:
> > + * The prepared transactions that were skipped because previously
> > + * two-phase was not enabled or are not covered by initial snapshot needs
> > + * to be sent later along with commit prepared and they must be before
> > + * this point.
> > AFTER:
> > + * The prepared transactions, that were skipped because previously
> > + * two-phase was not enabled or are not covered by initial snapshot, need
> > + * to be sent later along with commit prepared and they must be before
> > + * this point.
> >
>
> fixed.
>
> > (iv)
> >
> > src/backend/replication/logical/tablesync.c
> >
> > I think the convention used in Postgres code is to check for empty
> > Lists using "== NIL" and non-empty Lists using "!= NIL".
> >
> > BEFORE:
> > + if (table_states_not_ready && !last_start_times)
> > AFTER:
> > + if (table_states_not_ready != NIL && !last_start_times)
> >
> >
> > BEFORE:
> > + else if (!table_states_not_ready && last_start_times)
> > AFTER:
> > + else if (table_states_not_ready == NIL && last_start_times)
> >
>
> fixed.
>
> Also fixed comments from Vignesh:
>
> 1) This content is present in
> v87-0001-Add-option-to-set-two-phase-in-CREATE_REPLICATIO.patch and
> v87-0003-Add-support-for-prepared-transactions-to-built-i.patch, it
> can be removed from one of them
>        <varlistentry>
> +       <term><literal>TWO_PHASE</literal></term>
> +       <listitem>
> +        <para>
> +         Specify that this logical replication slot supports decoding
> of two-phase
> +         transactions. With this option, two-phase commands like
> +         <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT
> PREPARED</literal>
> +         and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
> +         The transaction will be decoded and transmitted at
> +         <literal>PREPARE TRANSACTION</literal> time.
> +        </para>
> +       </listitem>
> +      </varlistentry>
> +
> +      <varlistentry>
>
> I don't see this duplicate content.

Thanks for the updated patch.
The patch v89-0001-Add-option-to-set-two-phase-in-CREATE_REPLICATIO.patch
has the following:
+       <term><literal>TWO_PHASE</literal></term>
+       <listitem>
+        <para>
+         Specify that this logical replication slot supports decoding
of two-phase
+         transactions. With this option, two-phase commands like
+         <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT
PREPARED</literal>
+         and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+         The transaction will be decoded and transmitted at
+         <literal>PREPARE TRANSACTION</literal> time.
+        </para>
+       </listitem>
+      </varlistentry>

The patch v89-0003-Add-support-for-prepared-transactions-to-built-i.patch
has the following:
+       <term><literal>TWO_PHASE</literal></term>
+       <listitem>
+        <para>
+         Specify that this replication slot supports decode of two-phase
+         transactions. With this option, two-phase commands like
+         <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT
PREPARED</literal>
+         and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+         The transaction will be decoded and transmitted at
+         <literal>PREPARE TRANSACTION</literal> time.
+        </para>
+       </listitem>
+      </varlistentry>

We can remove one of them.

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