Add sequence synchronization for logical replication.

This patch introduces sequence synchronization. Sequences that are synced
will have 2 states:
   - INIT (needs [re]synchronizing)
   - READY (is already synchronized)

A new sequencesync worker is launched as needed to synchronize sequences.
A single sequencesync worker is responsible for synchronizing all
sequences. It begins by retrieving the list of sequences that are flagged
for synchronization, i.e., those in the INIT state. These sequences are
then processed in batches, allowing multiple entries to be synchronized
within a single transaction. The worker fetches the current sequence
values and page LSNs from the remote publisher, updates the corresponding
sequences on the local subscriber, and finally marks each sequence as
READY upon successful synchronization.

Sequence synchronization occurs in 3 places:
1) CREATE SUBSCRIPTION
    - The command syntax remains unchanged.
    - The subscriber retrieves sequences associated with publications.
    - Published sequences are added to pg_subscription_rel with INIT
      state.
    - Initiate the sequencesync worker to synchronize all sequences.

2) ALTER SUBSCRIPTION ... REFRESH PUBLICATION
    - The command syntax remains unchanged.
    - Dropped published sequences are removed from pg_subscription_rel.
    - Newly published sequences are added to pg_subscription_rel with INIT
      state.
    - Initiate the sequencesync worker to synchronize only newly added
      sequences.

3) ALTER SUBSCRIPTION ... REFRESH SEQUENCES
    - A new command introduced for PG19 by f0b3573c3a.
    - All sequences in pg_subscription_rel are reset to INIT state.
    - Initiate the sequencesync worker to synchronize all sequences.
    - Unlike "ALTER SUBSCRIPTION ... REFRESH PUBLICATION" command,
      addition and removal of missing sequences will not be done in this
      case.

Author: Vignesh C <vignesh21@gmail.com>
Reviewed-by: shveta malik <shveta.malik@gmail.com>
Reviewed-by: Hou Zhijie <houzj.fnst@fujitsu.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>
Reviewed-by: Peter Smith <smithpb2250@gmail.com>
Reviewed-by: Nisha Moond <nisha.moond412@gmail.com>
Reviewed-by: Shlok Kyal <shlok.kyal.oss@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CAA4eK1LC+KJiAkSrpE_NwvNdidw9F2os7GERUeSxSKv71gXysQ@mail.gmail.com

1 files changed, 9 insertions, 9 deletions

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index c23dee5231c..8d671b7a29d 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -112,7 +112,6 @@ static void init_params(ParseState *pstate, List *options, bool for_identity,
 						bool *is_called,
 						bool *need_seq_rewrite,
 						List **owned_by);
-static void do_setval(Oid relid, int64 next, bool iscalled);
 static void process_owned_by(Relation seqrel, List *owned_by, bool for_identity);
 
 
@@ -954,8 +953,8 @@ lastval(PG_FUNCTION_ARGS)
  * it is the only way to clear the is_called flag in an existing
  * sequence.
  */
-static void
-do_setval(Oid relid, int64 next, bool iscalled)
+void
+SetSequence(Oid relid, int64 next, bool iscalled)
 {
 	SeqTable	elm;
 	Relation	seqrel;
@@ -1056,7 +1055,7 @@ do_setval(Oid relid, int64 next, bool iscalled)
 
 /*
  * Implement the 2 arg setval procedure.
- * See do_setval for discussion.
+ * See SetSequence for discussion.
  */
 Datum
 setval_oid(PG_FUNCTION_ARGS)
@@ -1064,14 +1063,14 @@ setval_oid(PG_FUNCTION_ARGS)
 	Oid			relid = PG_GETARG_OID(0);
 	int64		next = PG_GETARG_INT64(1);
 
-	do_setval(relid, next, true);
+	SetSequence(relid, next, true);
 
 	PG_RETURN_INT64(next);
 }
 
 /*
  * Implement the 3 arg setval procedure.
- * See do_setval for discussion.
+ * See SetSequence for discussion.
  */
 Datum
 setval3_oid(PG_FUNCTION_ARGS)
@@ -1080,7 +1079,7 @@ setval3_oid(PG_FUNCTION_ARGS)
 	int64		next = PG_GETARG_INT64(1);
 	bool		iscalled = PG_GETARG_BOOL(2);
 
-	do_setval(relid, next, iscalled);
+	SetSequence(relid, next, iscalled);
 
 	PG_RETURN_INT64(next);
 }
@@ -1797,8 +1796,9 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
 /*
  * Return the sequence tuple along with its page LSN.
  *
- * This is primarily intended for use by pg_dump to gather sequence data
- * without needing to individually query each sequence relation.
+ * This is primarily used by pg_dump to efficiently collect sequence data
+ * without querying each sequence individually, and is also leveraged by
+ * logical replication while synchronizing sequences.
  */
 Datum
 pg_get_sequence_data(PG_FUNCTION_ARGS)