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>, Ajin Cherian <itsajin@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2021-05-10T03:31:11Z
Lists: pgsql-hackers 
On Thu, Apr 29, 2021 at 2:23 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Please find attached the latest patch set v74*
>
> Differences from v73* are:
>
> * Rebased to HEAD @ 2 days ago.
>
> * v74 addresses most of the feedback comments from Vignesh posts [1][2][3].
>

Thanks for the updated patch.
Few comments:
1) I felt skey[2] should be skey as we are just using one key here.

+       ScanKeyData skey[2];
+       SysScanDesc scan;
+       bool            has_subrels;
+
+       rel = table_open(SubscriptionRelRelationId, AccessShareLock);
+
+       ScanKeyInit(&skey[nkeys++],
+                               Anum_pg_subscription_rel_srsubid,
+                               BTEqualStrategyNumber, F_OIDEQ,
+                               ObjectIdGetDatum(subid));
+
+       scan = systable_beginscan(rel, InvalidOid, false,
+                                                         NULL, nkeys, skey);
+

2) I felt we can change lsn data type from Int64 to XLogRecPtr
+<varlistentry>
+<term>Int64</term>
+<listitem><para>
+                The LSN of the prepare.
+</para></listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Int64</term>
+<listitem><para>
+                The end LSN of the transaction.
+</para></listitem>
+</varlistentry>

3) I felt we can change lsn data type from Int32 to TransactionId
+<varlistentry>
+<term>Int32</term>
+<listitem><para>
+                Xid of the subtransaction (will be same as xid of the
transaction for top-level
+                transactions).
+</para></listitem>
+</varlistentry>

4) Should we change this to "The end LSN of the prepared transaction"
just to avoid any confusion of it meaning commit/rollback.
+<varlistentry>
+<term>Int64</term>
+<listitem><para>
+                The end LSN of the transaction.
+</para></listitem>
+</varlistentry>

Similar problems related to comments 2 and 3 are being discussed at
[1], we can change it accordingly based on the conclusion in the other
thread.
[1] - https://www.postgresql.org/message-id/flat/CAHut%2BPs2JsSd_OpBR9kXt1Rt4bwyXAjh875gUpFw6T210ttO7Q%40mail.gmail.com#cf2a85d0623dcadfbb1204a196681313

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