Expose sequence page LSN via pg_get_sequence_data.

This patch enhances the pg_get_sequence_data function to include the
page-level LSN (Log Sequence Number) of the sequence. This additional
metadata will be used by upcoming patches to support synchronization
of sequences during logical replication.

By exposing the LSN, we enable more accurate tracking of sequence
changes, which is essential for maintaining consistency across
replicated nodes.

Author: vignesh C <vignesh21@gmail.com>
Reviewed-by: shveta malik <shveta.malik@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://www.postgresql.org/message-id/CAA4eK1LC+KJiAkSrpE_NwvNdidw9F2os7GERUeSxSKv71gXysQ@mail.gmail.com

src/backend/commands/sequence.c

@@ -45,6 +45,7 @@
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
+#include "utils/pg_lsn.h"
 #include "utils/resowner.h"
 #include "utils/syscache.h"
 #include "utils/varlena.h"
@@ -1795,7 +1796,7 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
 
 
 /*
- * Return the sequence tuple.
+ * 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.
@@ -1803,7 +1804,7 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
 Datum
 pg_get_sequence_data(PG_FUNCTION_ARGS)
 {
-#define PG_GET_SEQUENCE_DATA_COLS	2
+#define PG_GET_SEQUENCE_DATA_COLS	3
 	Oid			relid = PG_GETARG_OID(0);
 	SeqTable	elm;
 	Relation	seqrel;
@@ -1818,6 +1819,8 @@ pg_get_sequence_data(PG_FUNCTION_ARGS)
 					   INT8OID, -1, 0);
 	TupleDescInitEntry(resultTupleDesc, (AttrNumber) 2, "is_called",
 					   BOOLOID, -1, 0);
+	TupleDescInitEntry(resultTupleDesc, (AttrNumber) 3, "page_lsn",
+					   LSNOID, -1, 0);
 	resultTupleDesc = BlessTupleDesc(resultTupleDesc);
 
 	init_sequence(relid, &elm, &seqrel);
@@ -1833,11 +1836,14 @@ pg_get_sequence_data(PG_FUNCTION_ARGS)
 		Buffer		buf;
 		HeapTupleData seqtuple;
 		Form_pg_sequence_data seq;
+		Page		page;
 
 		seq = read_seq_tuple(seqrel, &buf, &seqtuple);
+		page = BufferGetPage(buf);
 
 		values[0] = Int64GetDatum(seq->last_value);
 		values[1] = BoolGetDatum(seq->is_called);
+		values[2] = LSNGetDatum(PageGetLSN(page));
 
 		UnlockReleaseBuffer(buf);
 	}

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202510061
+#define CATALOG_VERSION_NO	202510062
 
 #endif

src/include/catalog/pg_proc.dat

@@ -3436,8 +3436,8 @@
 { oid => '6427', descr => 'return sequence tuple, for use by pg_dump',
   proname => 'pg_get_sequence_data', provolatile => 'v', proparallel => 'u',
   prorettype => 'record', proargtypes => 'regclass',
-  proallargtypes => '{regclass,int8,bool}', proargmodes => '{i,o,o}',
-  proargnames => '{sequence_oid,last_value,is_called}',
+  proallargtypes => '{regclass,int8,bool,pg_lsn}', proargmodes => '{i,o,o,o}',
+  proargnames => '{sequence_oid,last_value,is_called,page_lsn}',
   prosrc => 'pg_get_sequence_data' },
 
 { oid => '275', descr => 'return the next oid for a system table',

src/test/regress/expected/sequence.out

@@ -840,10 +840,10 @@ SELECT nextval('test_seq1');
 (1 row)
 
 -- pg_get_sequence_data
-SELECT * FROM pg_get_sequence_data('test_seq1');
- last_value | is_called 
-------------+-----------
-         10 | t
+SELECT last_value, is_called, page_lsn <= pg_current_wal_lsn() as lsn FROM pg_get_sequence_data('test_seq1');
+ last_value | is_called | lsn 
+------------+-----------+-----
+         10 | t         | t
 (1 row)
 
 DROP SEQUENCE test_seq1;

src/test/regress/sql/sequence.sql

@@ -414,6 +414,6 @@ SELECT nextval('test_seq1');
 SELECT nextval('test_seq1');
 
 -- pg_get_sequence_data
-SELECT * FROM pg_get_sequence_data('test_seq1');
+SELECT last_value, is_called, page_lsn <= pg_current_wal_lsn() as lsn FROM pg_get_sequence_data('test_seq1');
 
 DROP SEQUENCE test_seq1;