Horton

Re: Logical Replication of sequences

Peter Smith <smithpb2250@gmail.com>

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From: Peter Smith <smithpb2250@gmail.com>
To: vignesh C <vignesh21@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Euler Taveira <euler@eulerto.com>, Michael Paquier <michael@paquier.xyz>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Hou, Zhijie/侯 志杰 <houzj.fnst@fujitsu.com>, "Jonathan S. Katz" <jkatz@postgresql.org>
Date: 2024-07-26T06:16:30Z
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. Doc: Add documentation for sequence synchronization.

  2. Remove unused assignment in CREATE PUBLICATION grammar.

  3. Add seq_sync_error_count to subscription statistics.

  4. Fix few issues in commit 5509055d69.

  5. Add sequence synchronization for logical replication.

  6. Add worker type argument to logical replication worker functions.

  7. Introduce "REFRESH SEQUENCES" for subscriptions.

  8. Refactor logical worker synchronization code into a separate file.

  9. Standardize use of REFRESH PUBLICATION in code and messages.

  10. Add "ALL SEQUENCES" support to publications.

  11. Expose sequence page LSN via pg_get_sequence_data.

  12. Resume conflict-relevant data retention automatically.

  13. Post-commit review fixes for 228c370868.

  14. Generate GUC tables from .dat file

Attachments

Hi Vignesh,

There are still pending changes from my previous review of the
0720-0003 patch [1], but here are some new review comments for your
latest patch v20240525-0003.

======
doc/src/sgml/catalogs.sgml

nitpick - fix plurals and tweak the description.

~~~

1.
   <para>
-   This catalog only contains tables known to the subscription after running
-   either <link linkend="sql-createsubscription"><command>CREATE
SUBSCRIPTION</command></link> or
-   <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION
... REFRESH
+   This catalog only contains tables and sequences known to the subscription
+   after running either
+   <link linkend="sql-createsubscription"><command>CREATE
SUBSCRIPTION</command></link>
+   or <link linkend="sql-altersubscription"><command>ALTER
SUBSCRIPTION ... REFRESH
    PUBLICATION</command></link>.
   </para>

Shouldn't this mention "REFRESH PUBLICATION SEQUENCES" too?

======
src/backend/commands/sequence.c

SetSequenceLastValue:
nitpick - maybe change: /log_cnt/new_log_cnt/ for consistency with the
other parameter, and to emphasise the old log_cnt is overwritten

======
src/backend/replication/logical/sequencesync.c

2.
+/*
+ * fetch_remote_sequence_data
+ *
+ * Fetch sequence data (current state) from the remote node, including
+ * the latest sequence value from the publisher and the Page LSN for the
+ * sequence.
+ */
+static int64
+fetch_remote_sequence_data(WalReceiverConn *conn, Oid remoteid,
+    int64 *log_cnt, XLogRecPtr *lsn)

2a.
Now you are also returning the 'log_cnt' but that is not mentioned by
the function comment.

~

2b.
Is it better to name these returned by-ref ptrs like 'ret_log_cnt',
and 'ret_lsn' to emphasise they are output variables? YMMV.

~~~

3.
+ /* Process the sequence. */
+ slot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
+ while (tuplestore_gettupleslot(res->tuplestore, true, false, slot))

This will have one-and-only-one tuple for the discovered sequence,
won't it? So, why is this a while loop?

======
src/include/commands/sequence.h

nitpick - maybe change: /log_cnt/new_log_cnt/ (same as earlier in this post)

======
src/test/subscription/t/034_sequences.pl

4.
Q. Should we be suspicious that log_cnt changes from '32' to '31', or
is there a valid explanation? It smells like some calculation is
off-by-one, but without debugging I can't tell if it is right or
wrong.

======
Please also see the attached diffs patch, which implements the
nitpicks mentioned above.

======
[1] 0720-0003 review -
https://www.postgresql.org/message-id/CAHut%2BPsfsfzyBrmo8E43qFMp9_bmen2tuCsNYN8sX%3Dfa86SdfA%40mail.gmail.com

Kind Regards,
Peter Smith.
Fujitsu Australia