v20240625-0001-Introduce-pg_sequence_state-and-SetSequenc.patch

From 4c6daeb460ace314b220a9bf1a5ff59f2afd8ce1 Mon Sep 17 00:00:00 2001
From: Vignesh C <vignesh21@gmail.com>
Date: Tue, 11 Jun 2024 12:15:16 +0530
Subject: [PATCH v20240625 1/3] Introduce pg_sequence_state and SetSequence
 functions for enhanced sequence management

This patch introduces new functionalities to PostgreSQL:
- pg_sequence_state allows retrieval of sequence values using LSN.
- SetSequence enables updating sequences with user-specified values.
---
 src/backend/commands/sequence.c | 161 ++++++++++++++++++++++++++++++--
 src/include/catalog/pg_proc.dat |   8 ++
 src/include/commands/sequence.h |   1 +
 3 files changed, 162 insertions(+), 8 deletions(-)

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index 28f8522264..57453a7356 100644
--- a/src/backend/commands/sequence.c
+++ b/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"
@@ -102,7 +103,8 @@ static Relation lock_and_open_sequence(SeqTable seq);
 static void create_seq_hashtable(void);
 static void init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel);
 static Form_pg_sequence_data read_seq_tuple(Relation rel,
-											Buffer *buf, HeapTuple seqdatatuple);
+											Buffer *buf, HeapTuple seqdatatuple,
+											XLogRecPtr *lsn);
 static void init_params(ParseState *pstate, List *options, bool for_identity,
 						bool isInit,
 						Form_pg_sequence seqform,
@@ -277,7 +279,7 @@ ResetSequence(Oid seq_relid)
 	 * indeed a sequence.
 	 */
 	init_sequence(seq_relid, &elm, &seq_rel);
-	(void) read_seq_tuple(seq_rel, &buf, &seqdatatuple);
+	(void) read_seq_tuple(seq_rel, &buf, &seqdatatuple, NULL);
 
 	pgstuple = SearchSysCache1(SEQRELID, ObjectIdGetDatum(seq_relid));
 	if (!HeapTupleIsValid(pgstuple))
@@ -328,6 +330,80 @@ ResetSequence(Oid seq_relid)
 	sequence_close(seq_rel, NoLock);
 }
 
+/*
+ * Set a sequence to a specified internal state.
+ *
+ * Caller is assumed to have acquired AccessExclusiveLock on the sequence,
+ * which must not be released until end of transaction.  Caller is also
+ * responsible for permissions checking.
+ */
+void
+SetSequence(Oid seq_relid, int64 value)
+{
+	SeqTable        elm;
+	Relation        seqrel;
+	Buffer          buf;
+	HeapTupleData seqdatatuple;
+	Form_pg_sequence_data seq;
+
+	/* open and lock sequence */
+	init_sequence(seq_relid, &elm, &seqrel);
+
+	/* lock page' buffer and read tuple */
+	seq = read_seq_tuple(seqrel, &buf, &seqdatatuple, NULL);
+
+	/* check the comment above nextval_internal()'s equivalent call. */
+	if (RelationNeedsWAL(seqrel))
+	{
+		GetTopTransactionId();
+
+		if (XLogLogicalInfoActive())
+			GetCurrentTransactionId();
+	}
+
+	/* ready to change the on-disk (or really, in-buffer) tuple */
+	START_CRIT_SECTION();
+
+	seq->last_value = value;
+	seq->is_called = true;
+	seq->log_cnt = 0;
+
+	MarkBufferDirty(buf);
+
+	/* XLOG stuff */
+	if (RelationNeedsWAL(seqrel))
+	{
+		xl_seq_rec      xlrec;
+		XLogRecPtr      recptr;
+		Page            page = BufferGetPage(buf);
+
+		XLogBeginInsert();
+		XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);
+
+		xlrec.locator = seqrel->rd_locator;
+
+		XLogRegisterData((char *) &xlrec, sizeof(xl_seq_rec));
+		XLogRegisterData((char *) seqdatatuple.t_data, seqdatatuple.t_len);
+
+		/* allow filtering by origin on a sequence update */
+		XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
+
+		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG);
+
+		PageSetLSN(page, recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	UnlockReleaseBuffer(buf);
+
+	/* Clear local cache so that we don't think we have cached numbers */
+	/* Note that we do not change the currval() state */
+	elm->cached = elm->last;
+
+	relation_close(seqrel, NoLock);
+}
+
 /*
  * Initialize a sequence's relation with the specified tuple as content
  *
@@ -476,7 +552,7 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
 	seqform = (Form_pg_sequence) GETSTRUCT(seqtuple);
 
 	/* lock page buffer and read tuple into new sequence structure */
-	(void) read_seq_tuple(seqrel, &buf, &datatuple);
+	(void) read_seq_tuple(seqrel, &buf, &datatuple, NULL);
 
 	/* copy the existing sequence data tuple, so it can be modified locally */
 	newdatatuple = heap_copytuple(&datatuple);
@@ -551,7 +627,7 @@ SequenceChangePersistence(Oid relid, char newrelpersistence)
 	if (RelationNeedsWAL(seqrel))
 		GetTopTransactionId();
 
-	(void) read_seq_tuple(seqrel, &buf, &seqdatatuple);
+	(void) read_seq_tuple(seqrel, &buf, &seqdatatuple, NULL);
 	RelationSetNewRelfilenumber(seqrel, newrelpersistence);
 	fill_seq_with_data(seqrel, &seqdatatuple);
 	UnlockReleaseBuffer(buf);
@@ -680,7 +756,7 @@ nextval_internal(Oid relid, bool check_permissions)
 	ReleaseSysCache(pgstuple);
 
 	/* lock page buffer and read tuple */
-	seq = read_seq_tuple(seqrel, &buf, &seqdatatuple);
+	seq = read_seq_tuple(seqrel, &buf, &seqdatatuple, NULL);
 	page = BufferGetPage(buf);
 
 	last = next = result = seq->last_value;
@@ -976,7 +1052,7 @@ do_setval(Oid relid, int64 next, bool iscalled)
 	PreventCommandIfParallelMode("setval()");
 
 	/* lock page buffer and read tuple */
-	seq = read_seq_tuple(seqrel, &buf, &seqdatatuple);
+	seq = read_seq_tuple(seqrel, &buf, &seqdatatuple, NULL);
 
 	if ((next < minv) || (next > maxv))
 		ereport(ERROR,
@@ -1180,7 +1256,8 @@ init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel)
  * Function's return value points to the data payload of the tuple
  */
 static Form_pg_sequence_data
-read_seq_tuple(Relation rel, Buffer *buf, HeapTuple seqdatatuple)
+read_seq_tuple(Relation rel, Buffer *buf, HeapTuple seqdatatuple,
+			   XLogRecPtr *lsn)
 {
 	Page		page;
 	ItemId		lp;
@@ -1197,6 +1274,13 @@ read_seq_tuple(Relation rel, Buffer *buf, HeapTuple seqdatatuple)
 		elog(ERROR, "bad magic number in sequence \"%s\": %08X",
 			 RelationGetRelationName(rel), sm->magic);
 
+	/*
+	 * If the caller requested it, set the page LSN. This allows deciding
+	 * which sequence changes are before/after the returned sequence state.
+	 */
+	if (lsn)
+		*lsn = PageGetLSN(page);
+
 	lp = PageGetItemId(page, FirstOffsetNumber);
 	Assert(ItemIdIsNormal(lp));
 
@@ -1804,7 +1888,7 @@ pg_sequence_last_value(PG_FUNCTION_ARGS)
 		HeapTupleData seqtuple;
 		Form_pg_sequence_data seq;
 
-		seq = read_seq_tuple(seqrel, &buf, &seqtuple);
+		seq = read_seq_tuple(seqrel, &buf, &seqtuple, NULL);
 
 		is_called = seq->is_called;
 		result = seq->last_value;
@@ -1819,6 +1903,67 @@ pg_sequence_last_value(PG_FUNCTION_ARGS)
 		PG_RETURN_NULL();
 }
 
+/*
+ * Return the current on-disk state of the sequence.
+ *
+ * Note: This is roughly equivalent to selecting the data from the sequence,
+ * except that it also returns the page LSN.
+ */
+Datum
+pg_sequence_state(PG_FUNCTION_ARGS)
+{
+	Oid			relid = PG_GETARG_OID(0);
+	SeqTable	elm;
+	Relation	seqrel;
+	Buffer		buf;
+	HeapTupleData seqtuple;
+	Form_pg_sequence_data seq;
+	Datum		result;
+
+	int64		last_value;
+	int64		log_cnt;
+	bool		is_called;
+	XLogRecPtr	lsn;
+
+	TupleDesc	tupdesc;
+	HeapTuple	tuple;
+	Datum		values[4];
+	bool		nulls[4];
+
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	/* open and lock sequence */
+	init_sequence(relid, &elm, &seqrel);
+
+	if (pg_class_aclcheck(elm->relid, GetUserId(),
+						  ACL_SELECT | ACL_USAGE) != ACLCHECK_OK)
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("permission denied for sequence %s",
+						RelationGetRelationName(seqrel))));
+
+	seq = read_seq_tuple(seqrel, &buf, &seqtuple, &lsn);
+
+	is_called = seq->is_called;
+	last_value = seq->last_value;
+	log_cnt = seq->log_cnt;
+
+	UnlockReleaseBuffer(buf);
+	relation_close(seqrel, NoLock);
+
+	values[0] = LSNGetDatum(lsn);
+	values[1] = Int64GetDatum(last_value);
+	values[2] = Int64GetDatum(log_cnt);
+	values[3] = BoolGetDatum(is_called);
+
+	memset(nulls, 0, sizeof(nulls));
+
+	tuple = heap_form_tuple(tupdesc, values, nulls);
+	result = HeapTupleGetDatum(tuple);
+
+	PG_RETURN_DATUM(result);
+}
 
 void
 seq_redo(XLogReaderState *record)
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 6a5476d3c4..990ef2f836 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -3329,6 +3329,14 @@
   proname => 'pg_sequence_last_value', provolatile => 'v', proparallel => 'u',
   prorettype => 'int8', proargtypes => 'regclass',
   prosrc => 'pg_sequence_last_value' },
+{ oid => '6313',
+  descr => 'current on-disk sequence state',
+  proname => 'pg_sequence_state', provolatile => 'v',
+  prorettype => 'record', proargtypes => 'regclass',
+  proallargtypes => '{regclass,pg_lsn,int8,int8,bool}',
+  proargmodes => '{i,o,o,o,o}',
+  proargnames => '{seq_oid,page_lsn,last_value,log_cnt,is_called}',
+  prosrc => 'pg_sequence_state' },
 
 { oid => '275', descr => 'return the next oid for a system table',
   proname => 'pg_nextoid', provolatile => 'v', proparallel => 'u',
diff --git a/src/include/commands/sequence.h b/src/include/commands/sequence.h
index e88cbee3b5..fad731a733 100644
--- a/src/include/commands/sequence.h
+++ b/src/include/commands/sequence.h
@@ -60,6 +60,7 @@ extern ObjectAddress AlterSequence(ParseState *pstate, AlterSeqStmt *stmt);
 extern void SequenceChangePersistence(Oid relid, char newrelpersistence);
 extern void DeleteSequenceTuple(Oid relid);
 extern void ResetSequence(Oid seq_relid);
+extern void SetSequence(Oid seq_relid, int64 value);
 extern void ResetSequenceCaches(void);
 
 extern void seq_redo(XLogReaderState *record);
-- 
2.34.1