7 files changed, 72 insertions, 7 deletions

diff --git a/src/backend/storage/ipc/sinvaladt.c b/src/backend/storage/ipc/sinvaladt.c
index 59310b708fb..4a20fe7ebee 100644
--- a/src/backend/storage/ipc/sinvaladt.c
+++ b/src/backend/storage/ipc/sinvaladt.c
@@ -404,17 +404,20 @@ BackendIdGetProc(int backendID)
 
 /*
  * BackendIdGetTransactionIds
- *		Get the xid and xmin of the backend. The result may be out of date
- *		arbitrarily quickly, so the caller must be careful about how this
- *		information is used.
+ *		Get the xid, xmin, nsubxid and overflow status of the backend. The
+ *		result may be out of date arbitrarily quickly, so the caller must be
+ *		careful about how this information is used.
  */
 void
-BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmin)
+BackendIdGetTransactionIds(int backendID, TransactionId *xid,
+						   TransactionId *xmin, int *nsubxid, bool *overflowed)
 {
 	SISeg	   *segP = shmInvalBuffer;
 
 	*xid = InvalidTransactionId;
 	*xmin = InvalidTransactionId;
+	*nsubxid = 0;
+	*overflowed = false;
 
 	/* Need to lock out additions/removals of backends */
 	LWLockAcquire(SInvalWriteLock, LW_SHARED);
@@ -428,6 +431,8 @@ BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmi
 		{
 			*xid = proc->xid;
 			*xmin = proc->xmin;
+			*nsubxid = proc->subxidStatus.count;
+			*overflowed = proc->subxidStatus.overflowed;
 		}
 	}
 
diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c
index 1146a6c33cd..7ecf467b8cd 100644
--- a/src/backend/utils/activity/backend_status.c
+++ b/src/backend/utils/activity/backend_status.c
@@ -855,7 +855,9 @@ pgstat_read_current_status(void)
 			localentry->backend_id = i;
 			BackendIdGetTransactionIds(i,
 									   &localentry->backend_xid,
-									   &localentry->backend_xmin);
+									   &localentry->backend_xmin,
+									   &localentry->backend_subxact_count,
+									   &localentry->backend_subxact_overflowed);
 
 			localentry++;
 			localappname += NAMEDATALEN;
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 04a5a990025..46f98fd67f5 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -687,6 +687,44 @@ pg_stat_get_backend_userid(PG_FUNCTION_ARGS)
 	PG_RETURN_OID(beentry->st_userid);
 }
 
+Datum
+pg_stat_get_backend_subxact(PG_FUNCTION_ARGS)
+{
+#define PG_STAT_GET_SUBXACT_COLS	2
+	TupleDesc	tupdesc;
+	Datum		values[PG_STAT_GET_SUBXACT_COLS];
+	bool		nulls[PG_STAT_GET_SUBXACT_COLS];
+	int32		beid = PG_GETARG_INT32(0);
+	LocalPgBackendStatus *local_beentry;
+
+	/* Initialise values and NULL flags arrays */
+	MemSet(values, 0, sizeof(values));
+	MemSet(nulls, 0, sizeof(nulls));
+
+	/* Initialise attributes information in the tuple descriptor */
+	tupdesc = CreateTemplateTupleDesc(PG_STAT_GET_SUBXACT_COLS);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "subxact_count",
+					   INT4OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "subxact_overflow",
+					   BOOLOID, -1, 0);
+
+	BlessTupleDesc(tupdesc);
+
+	if ((local_beentry = pgstat_fetch_stat_local_beentry(beid)) != NULL)
+	{
+		/* Fill values and NULLs */
+		values[0] = Int32GetDatum(local_beentry->backend_subxact_count);
+		values[1] = BoolGetDatum(local_beentry->backend_subxact_overflowed);
+	}
+	else
+	{
+		nulls[0] = true;
+		nulls[1] = true;
+	}
+
+	/* Returns the record as Datum */
+	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
+}
 
 Datum
 pg_stat_get_backend_activity(PG_FUNCTION_ARGS)
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 5cb12437a67..094f59f82db 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202212131
+#define CATALOG_VERSION_NO	202212191
 
 #endif
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 719599649a9..d763419c0de 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5441,6 +5441,13 @@
   proname => 'pg_stat_get_backend_dbid', provolatile => 's', proparallel => 'r',
   prorettype => 'oid', proargtypes => 'int4',
   prosrc => 'pg_stat_get_backend_dbid' },
+{ oid => '6107', descr => 'statistics: get subtransaction status of backend',
+  proname => 'pg_stat_get_backend_subxact', provolatile => 's', proparallel => 'r',
+  prorettype => 'record', proargtypes => 'int4',
+  proallargtypes => '{int4,int4,bool}',
+  proargmodes => '{i,o,o}',
+  proargnames => '{bid,subxact_count,subxact_overflowed}',
+  prosrc => 'pg_stat_get_backend_subxact' },
 { oid => '1939', descr => 'statistics: user ID of backend',
   proname => 'pg_stat_get_backend_userid', provolatile => 's',
   proparallel => 'r', prorettype => 'oid', proargtypes => 'int4',
diff --git a/src/include/storage/sinvaladt.h b/src/include/storage/sinvaladt.h
index 91e24189a7a..bf739ebdba7 100644
--- a/src/include/storage/sinvaladt.h
+++ b/src/include/storage/sinvaladt.h
@@ -32,7 +32,9 @@ extern Size SInvalShmemSize(void);
 extern void CreateSharedInvalidationState(void);
 extern void SharedInvalBackendInit(bool sendOnly);
 extern PGPROC *BackendIdGetProc(int backendID);
-extern void BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmin);
+extern void BackendIdGetTransactionIds(int backendID, TransactionId *xid,
+									   TransactionId *xmin, int *nsubxid,
+									   bool *overflowed);
 
 extern void SIInsertDataEntries(const SharedInvalidationMessage *data, int n);
 extern int	SIGetDataEntries(SharedInvalidationMessage *data, int datasize);
diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h
index b582b46e9f9..e076adcaa82 100644
--- a/src/include/utils/backend_status.h
+++ b/src/include/utils/backend_status.h
@@ -266,6 +266,17 @@ typedef struct LocalPgBackendStatus
 	 * not.
 	 */
 	TransactionId backend_xmin;
+
+	/*
+	 * Number of cached subtransactions in the current session.
+	 */
+	int	backend_subxact_count;
+
+	/*
+	 * The number of subtransactions in the current session exceeded the cached
+	 * subtransaction limit.
+	 */
+	bool backend_subxact_overflowed;
 } LocalPgBackendStatus;