Horton

Re: Logical Replication of sequences

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: vignesh C <vignesh21@gmail.com>
Cc: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Dilip Kumar <dilipbalaut@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Chao Li <li.evan.chao@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Euler Taveira <euler@eulerto.com>, Michael Paquier <michael@paquier.xyz>, "Jonathan S. Katz" <jkatz@postgresql.org>, Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>
Date: 2025-10-21T09:37:13Z
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

Few trivial comments on 001:

patch001:

1)
FetchRelationStates
  /* Fetch tables and sequences that are in non-ready state. */
- rstates = GetSubscriptionRelations(MySubscription->oid, true);
+ rstates = GetSubscriptionRelations(MySubscription->oid, true, false,
+    true);

We are passing get_Sequenecs as false, we should update comment to get
rid of 'sequences;

2)
+ /*
+ * XXX The walsender currently does not transmit the relkind of the remote
+ * relation when replicating changes. Since we support replicating only
+ * table changes at present, we default to initializing relkind as
+ * RELKIND_RELATION.
+ */
+ entry->remoterel.relkind = remoterel->relkind
+ ? remoterel->relkind : RELKIND_RELATION;

Shall we also mention that currently this is used or needed only for
CheckSubscriptionRelkind().

~~

Few on 002:

3)
sequencesync.c:

+ * Executing the following command resets all sequences in the subscription to
+ * state DATASYNC, triggering re-synchronization:
+ * ALTER SUBSCRIPTION ... REFRESH SEQUENCES

+ * Sequence state transitions follow this pattern:
+ *   INIT / DATASYNC → READY

These comments need correction. We no longer use DATASYNC state for seq.

4)
+ * To avoid creating too many transactions, up to MAX_SEQUENCES_SYNC_PER_BATCH
+ * (100) sequences are synchronized per transaction. The locks on the sequence

We can avoid writing 100 here. Mention of macro is enough.

5)
I had some 250 sequences; dropped one on pub, and ran 'refresh
sequences' on sub, noticed few issues:

a) Seqsync worker logged below but actually did not remove it. It
seems it is some pending log from previous implementation:

LOG:  sequences not found on publisher removed from resynchronization:
("public.myseq250")

b) It kept on restarting the seq sync worker very fast. It should have
waited for wal_retrieve_retry_interval (which is 5s in my env) to
attempt restarting, isn't it? Logs:
----
14:27:53.492 IST [72327] LOG:  logical replication sequence
synchronization worker for subscription "sub1" has started
14:27:53.499 IST [72327] LOG:  logical replication sequence
synchronization for subscription "sub1" - total unsynchronized: 1
14:27:53.500 IST [72327] LOG:  logical replication sequence
synchronization for subscription "sub1" - batch #1 = 1 attempted, 0
succeeded, 0 skipped, 0 mismatched, 0 insufficient permission, 1
missing from publisher
14:27:53.500 IST [72327] LOG:  sequences not found on publisher
removed from resynchronization: ("public.myseq250")
14:27:53.500 IST [72327] LOG:  logical replication sequence
synchronization worker for subscription "sub1" has finished
14:27:53.503 IST [72329] LOG:  logical replication sequence
synchronization worker for subscription "sub1" has started
14:27:53.508 IST [72329] LOG:  logical replication sequence
synchronization for subscription "sub1" - total unsynchronized: 1
----

c) Should this case give a suggestion/HINT in log to run 'REFERSH PUB'
to correct sequence mapping.

thanks
Shveta