Replace BackendIds with 0-based ProcNumbers

Now that BackendId was just another index into the proc array, it was
redundant with the 0-based proc numbers used in other places. Replace
all usage of backend IDs with proc numbers.

The only place where the term "backend id" remains is in a few pgstat
functions that expose backend IDs at the SQL level. Those IDs are now
in fact 0-based ProcNumbers too, but the documentation still calls
them "backend ids". That term still seems appropriate to describe what
the numbers are, so I let it be.

One user-visible effect is that pg_temp_0 is now a valid temp schema
name, for backend with ProcNumber 0.

Reviewed-by: Andres Freund
Discussion: https://www.postgresql.org/message-id/8171f1aa-496f-46a6-afc3-c46fe7a9b407@iki.fi

12 files changed, 97 insertions, 97 deletions

diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c
index 3d3f7b06723..c91ed5a4b64 100644
--- a/src/backend/utils/activity/backend_status.c
+++ b/src/backend/utils/activity/backend_status.c
@@ -238,7 +238,7 @@ CreateSharedBackendStatus(void)
 
 /*
  * Initialize pgstats backend activity state, and set up our on-proc-exit
- * hook.  Called from InitPostgres and AuxiliaryProcessMain.  MyBackendId must
+ * hook.  Called from InitPostgres and AuxiliaryProcessMain.  MyProcNumber must
  * be set, but we must not have started any transaction yet (since the exit
  * hook must run after the last transaction exit).
  *
@@ -248,9 +248,9 @@ void
 pgstat_beinit(void)
 {
 	/* Initialize MyBEEntry */
-	Assert(MyBackendId != InvalidBackendId);
-	Assert(MyBackendId >= 1 && MyBackendId <= NumBackendStatSlots);
-	MyBEEntry = &BackendStatusArray[MyBackendId - 1];
+	Assert(MyProcNumber != INVALID_PROC_NUMBER);
+	Assert(MyProcNumber >= 0 && MyProcNumber < NumBackendStatSlots);
+	MyBEEntry = &BackendStatusArray[MyProcNumber];
 
 	/* Set up a process-exit hook to clean up */
 	on_shmem_exit(pgstat_beshutdown_hook, 0);
@@ -721,7 +721,7 @@ pgstat_read_current_status(void)
 #ifdef ENABLE_GSS
 	PgBackendGSSStatus *localgssstatus;
 #endif
-	int			i;
+	ProcNumber	procNumber;
 
 	if (localBackendStatusTable)
 		return;					/* already done */
@@ -764,7 +764,7 @@ pgstat_read_current_status(void)
 
 	beentry = BackendStatusArray;
 	localentry = localtable;
-	for (i = 1; i <= NumBackendStatSlots; i++)
+	for (procNumber = 0; procNumber < NumBackendStatSlots; procNumber++)
 	{
 		/*
 		 * Follow the protocol of retrying if st_changecount changes while we
@@ -830,17 +830,17 @@ pgstat_read_current_status(void)
 		if (localentry->backendStatus.st_procpid > 0)
 		{
 			/*
-			 * The BackendStatusArray index is exactly the BackendId of the
+			 * The BackendStatusArray index is exactly the ProcNumber of the
 			 * source backend.  Note that this means localBackendStatusTable
-			 * is in order by backend_id.  pgstat_get_beentry_by_backend_id()
+			 * is in order by proc_number.  pgstat_get_beentry_by_backend_id()
 			 * depends on that.
 			 */
-			localentry->backend_id = i;
-			BackendIdGetTransactionIds(i,
-									   &localentry->backend_xid,
-									   &localentry->backend_xmin,
-									   &localentry->backend_subxact_count,
-									   &localentry->backend_subxact_overflowed);
+			localentry->proc_number = procNumber;
+			ProcNumberGetTransactionIds(procNumber,
+										&localentry->backend_xid,
+										&localentry->backend_xmin,
+										&localentry->backend_subxact_count,
+										&localentry->backend_subxact_overflowed);
 
 			localentry++;
 			localappname += NAMEDATALEN;
@@ -1043,7 +1043,7 @@ pgstat_get_my_query_id(void)
  * cmp_lbestatus
  *
  *	Comparison function for bsearch() on an array of LocalPgBackendStatus.
- *	The backend_id field is used to compare the arguments.
+ *	The proc_number field is used to compare the arguments.
  * ----------
  */
 static int
@@ -1052,17 +1052,17 @@ cmp_lbestatus(const void *a, const void *b)
 	const LocalPgBackendStatus *lbestatus1 = (const LocalPgBackendStatus *) a;
 	const LocalPgBackendStatus *lbestatus2 = (const LocalPgBackendStatus *) b;
 
-	return lbestatus1->backend_id - lbestatus2->backend_id;
+	return lbestatus1->proc_number - lbestatus2->proc_number;
 }
 
 /* ----------
- * pgstat_get_beentry_by_backend_id() -
+ * pgstat_get_beentry_by_proc_number() -
  *
  *	Support function for the SQL-callable pgstat* functions. Returns
  *	our local copy of the current-activity entry for one backend,
  *	or NULL if the given beid doesn't identify any known session.
  *
- *	The beid argument is the BackendId of the desired session
+ *	The argument is the ProcNumber of the desired session
  *	(note that this is unlike pgstat_get_local_beentry_by_index()).
  *
  *	NB: caller is responsible for a check if the user is permitted to see
@@ -1070,9 +1070,9 @@ cmp_lbestatus(const void *a, const void *b)
  * ----------
  */
 PgBackendStatus *
-pgstat_get_beentry_by_backend_id(BackendId beid)
+pgstat_get_beentry_by_proc_number(ProcNumber procNumber)
 {
-	LocalPgBackendStatus *ret = pgstat_get_local_beentry_by_backend_id(beid);
+	LocalPgBackendStatus *ret = pgstat_get_local_beentry_by_proc_number(procNumber);
 
 	if (ret)
 		return &ret->backendStatus;
@@ -1082,12 +1082,12 @@ pgstat_get_beentry_by_backend_id(BackendId beid)
 
 
 /* ----------
- * pgstat_get_local_beentry_by_backend_id() -
+ * pgstat_get_local_beentry_by_proc_number() -
  *
- *	Like pgstat_get_beentry_by_backend_id() but with locally computed additions
+ *	Like pgstat_get_beentry_by_proc_number() but with locally computed additions
  *	(like xid and xmin values of the backend)
  *
- *	The beid argument is the BackendId of the desired session
+ *	The argument is the ProcNumber of the desired session
  *	(note that this is unlike pgstat_get_local_beentry_by_index()).
  *
  *	NB: caller is responsible for checking if the user is permitted to see this
@@ -1095,7 +1095,7 @@ pgstat_get_beentry_by_backend_id(BackendId beid)
  * ----------
  */
 LocalPgBackendStatus *
-pgstat_get_local_beentry_by_backend_id(BackendId beid)
+pgstat_get_local_beentry_by_proc_number(ProcNumber procNumber)
 {
 	LocalPgBackendStatus key;
 
@@ -1105,7 +1105,7 @@ pgstat_get_local_beentry_by_backend_id(BackendId beid)
 	 * Since the localBackendStatusTable is in order by backend_id, we can use
 	 * bsearch() to search it efficiently.
 	 */
-	key.backend_id = beid;
+	key.proc_number = procNumber;
 	return bsearch(&key, localBackendStatusTable, localNumBackends,
 				   sizeof(LocalPgBackendStatus), cmp_lbestatus);
 }
diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index 2df025d50aa..3e851032786 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -306,7 +306,7 @@ pg_tablespace_size_name(PG_FUNCTION_ARGS)
  * is no check here or at the call sites for that.
  */
 static int64
-calculate_relation_size(RelFileLocator *rfn, BackendId backend, ForkNumber forknum)
+calculate_relation_size(RelFileLocator *rfn, ProcNumber backend, ForkNumber forknum)
 {
 	int64		totalsize = 0;
 	char	   *relationpath;
@@ -951,7 +951,7 @@ pg_relation_filepath(PG_FUNCTION_ARGS)
 	HeapTuple	tuple;
 	Form_pg_class relform;
 	RelFileLocator rlocator;
-	BackendId	backend;
+	ProcNumber	backend;
 	char	   *path;
 
 	tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
@@ -996,21 +996,21 @@ pg_relation_filepath(PG_FUNCTION_ARGS)
 	{
 		case RELPERSISTENCE_UNLOGGED:
 		case RELPERSISTENCE_PERMANENT:
-			backend = InvalidBackendId;
+			backend = INVALID_PROC_NUMBER;
 			break;
 		case RELPERSISTENCE_TEMP:
 			if (isTempOrTempToastNamespace(relform->relnamespace))
-				backend = BackendIdForTempRelations();
+				backend = ProcNumberForTempRelations();
 			else
 			{
 				/* Do it the hard way. */
-				backend = GetTempNamespaceBackendId(relform->relnamespace);
-				Assert(backend != InvalidBackendId);
+				backend = GetTempNamespaceProcNumber(relform->relnamespace);
+				Assert(backend != INVALID_PROC_NUMBER);
 			}
 			break;
 		default:
 			elog(ERROR, "invalid relpersistence: %c", relform->relpersistence);
-			backend = InvalidBackendId; /* placate compiler */
+			backend = INVALID_PROC_NUMBER;	/* placate compiler */
 			break;
 	}
 
diff --git a/src/backend/utils/adt/lockfuncs.c b/src/backend/utils/adt/lockfuncs.c
index bbe5cc0806e..8624470b1d9 100644
--- a/src/backend/utils/adt/lockfuncs.c
+++ b/src/backend/utils/adt/lockfuncs.c
@@ -73,15 +73,16 @@ typedef struct
  * This is currently only used in pg_lock_status, so we put it here.
  */
 static Datum
-VXIDGetDatum(BackendId bid, LocalTransactionId lxid)
+VXIDGetDatum(ProcNumber procNumber, LocalTransactionId lxid)
 {
 	/*
-	 * The representation is "<bid>/<lxid>", decimal and unsigned decimal
-	 * respectively.  Note that elog.c also knows how to format a vxid.
+	 * The representation is "<procNumber>/<lxid>", decimal and unsigned
+	 * decimal respectively.  Note that elog.c also knows how to format a
+	 * vxid.
 	 */
 	char		vxidstr[32];
 
-	snprintf(vxidstr, sizeof(vxidstr), "%d/%u", bid, lxid);
+	snprintf(vxidstr, sizeof(vxidstr), "%d/%u", procNumber, lxid);
 
 	return CStringGetTextDatum(vxidstr);
 }
@@ -353,7 +354,7 @@ pg_lock_status(PG_FUNCTION_ARGS)
 				break;
 		}
 
-		values[10] = VXIDGetDatum(instance->vxid.backendId, instance->vxid.localTransactionId);
+		values[10] = VXIDGetDatum(instance->vxid.procNumber, instance->vxid.localTransactionId);
 		if (instance->pid != 0)
 			values[11] = Int32GetDatum(instance->pid);
 		else
@@ -419,7 +420,7 @@ pg_lock_status(PG_FUNCTION_ARGS)
 		nulls[9] = true;		/* objsubid */
 
 		/* lock holder */
-		values[10] = VXIDGetDatum(xact->vxid.backendId,
+		values[10] = VXIDGetDatum(xact->vxid.procNumber,
 								  xact->vxid.localTransactionId);
 		if (xact->pid != 0)
 			values[11] = Int32GetDatum(xact->pid);
diff --git a/src/backend/utils/adt/mcxtfuncs.c b/src/backend/utils/adt/mcxtfuncs.c
index a7267dc15d1..c29320b3785 100644
--- a/src/backend/utils/adt/mcxtfuncs.c
+++ b/src/backend/utils/adt/mcxtfuncs.c
@@ -146,7 +146,7 @@ pg_log_backend_memory_contexts(PG_FUNCTION_ARGS)
 {
 	int			pid = PG_GETARG_INT32(0);
 	PGPROC	   *proc;
-	BackendId	backendId = InvalidBackendId;
+	ProcNumber	procNumber = INVALID_PROC_NUMBER;
 
 	/*
 	 * See if the process with given pid is a backend or an auxiliary process.
@@ -175,9 +175,8 @@ pg_log_backend_memory_contexts(PG_FUNCTION_ARGS)
 		PG_RETURN_BOOL(false);
 	}
 
-	if (proc != NULL)
-		backendId = GetBackendIdFromPGProc(proc);
-	if (SendProcSignal(pid, PROCSIG_LOG_MEMORY_CONTEXT, backendId) < 0)
+	procNumber = GetNumberFromPGProc(proc);
+	if (SendProcSignal(pid, PROCSIG_LOG_MEMORY_CONTEXT, procNumber) < 0)
 	{
 		/* Again, just a warning to allow loops */
 		ereport(WARNING,
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 30a20635057..d1e9aa8290f 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -213,7 +213,7 @@ pg_stat_get_backend_idset(PG_FUNCTION_ARGS)
 		/* do when there is more left to send */
 		LocalPgBackendStatus *local_beentry = pgstat_get_local_beentry_by_index(fctx[0]);
 
-		SRF_RETURN_NEXT(funcctx, Int32GetDatum(local_beentry->backend_id));
+		SRF_RETURN_NEXT(funcctx, Int32GetDatum(local_beentry->proc_number));
 	}
 	else
 	{
@@ -669,10 +669,10 @@ pg_backend_pid(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_pid(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		PG_RETURN_NULL();
 
 	PG_RETURN_INT32(beentry->st_procpid);
@@ -682,10 +682,10 @@ pg_stat_get_backend_pid(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_dbid(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		PG_RETURN_NULL();
 
 	PG_RETURN_OID(beentry->st_databaseid);
@@ -695,10 +695,10 @@ pg_stat_get_backend_dbid(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_userid(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		PG_RETURN_NULL();
 
 	PG_RETURN_OID(beentry->st_userid);
@@ -711,7 +711,7 @@ pg_stat_get_backend_subxact(PG_FUNCTION_ARGS)
 	TupleDesc	tupdesc;
 	Datum		values[PG_STAT_GET_SUBXACT_COLS] = {0};
 	bool		nulls[PG_STAT_GET_SUBXACT_COLS] = {0};
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	LocalPgBackendStatus *local_beentry;
 
 	/* Initialise attributes information in the tuple descriptor */
@@ -723,7 +723,7 @@ pg_stat_get_backend_subxact(PG_FUNCTION_ARGS)
 
 	BlessTupleDesc(tupdesc);
 
-	if ((local_beentry = pgstat_get_local_beentry_by_backend_id(beid)) != NULL)
+	if ((local_beentry = pgstat_get_local_beentry_by_proc_number(procNumber)) != NULL)
 	{
 		/* Fill values and NULLs */
 		values[0] = Int32GetDatum(local_beentry->backend_subxact_count);
@@ -742,13 +742,13 @@ pg_stat_get_backend_subxact(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_activity(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 	const char *activity;
 	char	   *clipped_activity;
 	text	   *ret;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		activity = "<backend information not available>";
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		activity = "<insufficient privilege>";
@@ -767,12 +767,12 @@ pg_stat_get_backend_activity(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_wait_event_type(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 	PGPROC	   *proc;
 	const char *wait_event_type = NULL;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		wait_event_type = "<backend information not available>";
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		wait_event_type = "<insufficient privilege>";
@@ -788,12 +788,12 @@ pg_stat_get_backend_wait_event_type(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_wait_event(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 	PGPROC	   *proc;
 	const char *wait_event = NULL;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		wait_event = "<backend information not available>";
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		wait_event = "<insufficient privilege>";
@@ -810,11 +810,11 @@ pg_stat_get_backend_wait_event(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_activity_start(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	TimestampTz result;
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -836,11 +836,11 @@ pg_stat_get_backend_activity_start(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_xact_start(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	TimestampTz result;
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -858,11 +858,11 @@ pg_stat_get_backend_xact_start(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_start(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	TimestampTz result;
 	PgBackendStatus *beentry;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -880,13 +880,13 @@ pg_stat_get_backend_start(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_client_addr(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 	SockAddr	zero_clientaddr;
 	char		remote_host[NI_MAXHOST];
 	int			ret;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
@@ -925,13 +925,13 @@ pg_stat_get_backend_client_addr(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_backend_client_port(PG_FUNCTION_ARGS)
 {
-	int32		beid = PG_GETARG_INT32(0);
+	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
 	SockAddr	zero_clientaddr;
 	char		remote_port[NI_MAXSERV];
 	int			ret;
 
-	if ((beentry = pgstat_get_beentry_by_backend_id(beid)) == NULL)
+	if ((beentry = pgstat_get_beentry_by_proc_number(procNumber)) == NULL)
 		PG_RETURN_NULL();
 
 	else if (!HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
diff --git a/src/backend/utils/cache/inval.c b/src/backend/utils/cache/inval.c
index f59b07a70f8..816b883b6da 100644
--- a/src/backend/utils/cache/inval.c
+++ b/src/backend/utils/cache/inval.c
@@ -1453,8 +1453,8 @@ CacheInvalidateRelcacheByRelid(Oid relid)
  * replaying WAL as well as when creating it.
  *
  * Note: In order to avoid bloating SharedInvalidationMessage, we store only
- * three bytes of the backend ID using what would otherwise be padding space.
- * Thus, the maximum possible backend ID is 2^23-1.
+ * three bytes of the ProcNumber using what would otherwise be padding space.
+ * Thus, the maximum possible ProcNumber is 2^23-1.
  */
 void
 CacheInvalidateSmgr(RelFileLocatorBackend rlocator)
diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 50acae45298..37c37df56c1 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -1144,13 +1144,13 @@ retry:
 	{
 		case RELPERSISTENCE_UNLOGGED:
 		case RELPERSISTENCE_PERMANENT:
-			relation->rd_backend = InvalidBackendId;
+			relation->rd_backend = INVALID_PROC_NUMBER;
 			relation->rd_islocaltemp = false;
 			break;
 		case RELPERSISTENCE_TEMP:
 			if (isTempOrTempToastNamespace(relation->rd_rel->relnamespace))
 			{
-				relation->rd_backend = BackendIdForTempRelations();
+				relation->rd_backend = ProcNumberForTempRelations();
 				relation->rd_islocaltemp = true;
 			}
 			else
@@ -1159,18 +1159,18 @@ retry:
 				 * If it's a temp table, but not one of ours, we have to use
 				 * the slow, grotty method to figure out the owning backend.
 				 *
-				 * Note: it's possible that rd_backend gets set to MyBackendId
-				 * here, in case we are looking at a pg_class entry left over
-				 * from a crashed backend that coincidentally had the same
-				 * BackendId we're using.  We should *not* consider such a
-				 * table to be "ours"; this is why we need the separate
-				 * rd_islocaltemp flag.  The pg_class entry will get flushed
-				 * if/when we clean out the corresponding temp table namespace
-				 * in preparation for using it.
+				 * Note: it's possible that rd_backend gets set to
+				 * MyProcNumber here, in case we are looking at a pg_class
+				 * entry left over from a crashed backend that coincidentally
+				 * had the same ProcNumber we're using.  We should *not*
+				 * consider such a table to be "ours"; this is why we need the
+				 * separate rd_islocaltemp flag.  The pg_class entry will get
+				 * flushed if/when we clean out the corresponding temp table
+				 * namespace in preparation for using it.
 				 */
 				relation->rd_backend =
-					GetTempNamespaceBackendId(relation->rd_rel->relnamespace);
-				Assert(relation->rd_backend != InvalidBackendId);
+					GetTempNamespaceProcNumber(relation->rd_rel->relnamespace);
+				Assert(relation->rd_backend != INVALID_PROC_NUMBER);
 				relation->rd_islocaltemp = false;
 			}
 			break;
@@ -1896,7 +1896,7 @@ formrdesc(const char *relationName, Oid relationReltype,
 	relation->rd_newRelfilelocatorSubid = InvalidSubTransactionId;
 	relation->rd_firstRelfilelocatorSubid = InvalidSubTransactionId;
 	relation->rd_droppedSubid = InvalidSubTransactionId;
-	relation->rd_backend = InvalidBackendId;
+	relation->rd_backend = INVALID_PROC_NUMBER;
 	relation->rd_islocaltemp = false;
 
 	/*
@@ -3611,12 +3611,12 @@ RelationBuildLocalRelation(const char *relname,
 	{
 		case RELPERSISTENCE_UNLOGGED:
 		case RELPERSISTENCE_PERMANENT:
-			rel->rd_backend = InvalidBackendId;
+			rel->rd_backend = INVALID_PROC_NUMBER;
 			rel->rd_islocaltemp = false;
 			break;
 		case RELPERSISTENCE_TEMP:
 			Assert(isTempOrTempToastNamespace(relnamespace));
-			rel->rd_backend = BackendIdForTempRelations();
+			rel->rd_backend = ProcNumberForTempRelations();
 			rel->rd_islocaltemp = true;
 			break;
 		default:
diff --git a/src/backend/utils/error/csvlog.c b/src/backend/utils/error/csvlog.c
index 1d44d8a6a31..99a3d862250 100644
--- a/src/backend/utils/error/csvlog.c
+++ b/src/backend/utils/error/csvlog.c
@@ -152,8 +152,8 @@ write_csvlog(ErrorData *edata)
 
 	/* Virtual transaction id */
 	/* keep VXID format in sync with lockfuncs.c */
-	if (MyProc != NULL && MyProc->vxid.backendId != InvalidBackendId)
-		appendStringInfo(&buf, "%d/%u", MyProc->vxid.backendId, MyProc->vxid.lxid);
+	if (MyProc != NULL && MyProc->vxid.procNumber != INVALID_PROC_NUMBER)
+		appendStringInfo(&buf, "%d/%u", MyProc->vxid.procNumber, MyProc->vxid.lxid);
 	appendStringInfoChar(&buf, ',');
 
 	/* Transaction id */
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 149b4b8df13..8d4bc5fbc91 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -3076,18 +3076,18 @@ log_status_format(StringInfo buf, const char *format, ErrorData *edata)
 				break;
 			case 'v':
 				/* keep VXID format in sync with lockfuncs.c */
-				if (MyProc != NULL && MyProc->vxid.backendId != InvalidBackendId)
+				if (MyProc != NULL && MyProc->vxid.procNumber != INVALID_PROC_NUMBER)
 				{
 					if (padding != 0)
 					{
 						char		strfbuf[128];
 
 						snprintf(strfbuf, sizeof(strfbuf) - 1, "%d/%u",
-								 MyProc->vxid.backendId, MyProc->vxid.lxid);
+								 MyProc->vxid.procNumber, MyProc->vxid.lxid);
 						appendStringInfo(buf, "%*s", padding, strfbuf);
 					}
 					else
-						appendStringInfo(buf, "%d/%u", MyProc->vxid.backendId, MyProc->vxid.lxid);
+						appendStringInfo(buf, "%d/%u", MyProc->vxid.procNumber, MyProc->vxid.lxid);
 				}
 				else if (padding != 0)
 					appendStringInfoSpaces(buf,
diff --git a/src/backend/utils/error/jsonlog.c b/src/backend/utils/error/jsonlog.c
index 067d9e30b16..d52c2143033 100644
--- a/src/backend/utils/error/jsonlog.c
+++ b/src/backend/utils/error/jsonlog.c
@@ -197,9 +197,9 @@ write_jsonlog(ErrorData *edata)
 
 	/* Virtual transaction id */
 	/* keep VXID format in sync with lockfuncs.c */
-	if (MyProc != NULL && MyProc->vxid.backendId != InvalidBackendId)
+	if (MyProc != NULL && MyProc->vxid.procNumber != INVALID_PROC_NUMBER)
 		appendJSONKeyValueFmt(&buf, "vxid", true, "%d/%u",
-							  MyProc->vxid.backendId, MyProc->vxid.lxid);
+							  MyProc->vxid.procNumber, MyProc->vxid.lxid);
 
 	/* Transaction id */
 	appendJSONKeyValueFmt(&buf, "txid", false, "%u",
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 5eaee88d969..aea95c8a69b 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -22,7 +22,7 @@
 #include "libpq/libpq-be.h"
 #include "libpq/pqcomm.h"
 #include "miscadmin.h"
-#include "storage/backendid.h"
+#include "storage/procnumber.h"
 
 
 ProtocolVersion FrontendProtocol;
@@ -83,9 +83,9 @@ char		postgres_exec_path[MAXPGPATH];	/* full path to backend */
 /* note: currently this is not valid in backend processes */
 #endif
 
-BackendId	MyBackendId = InvalidBackendId;
+ProcNumber	MyProcNumber = INVALID_PROC_NUMBER;
 
-BackendId	ParallelLeaderBackendId = InvalidBackendId;
+ProcNumber	ParallelLeaderProcNumber = INVALID_PROC_NUMBER;
 
 Oid			MyDatabaseId = InvalidOid;
 
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
index a0916959b17..06735f66709 100644
--- a/src/backend/utils/time/snapmgr.c
+++ b/src/backend/utils/time/snapmgr.c
@@ -1154,7 +1154,7 @@ ExportSnapshot(Snapshot snapshot)
 	 * inside the transaction from 1.
 	 */
 	snprintf(path, sizeof(path), SNAPSHOT_EXPORT_DIR "/%08X-%08X-%d",
-			 MyProc->vxid.backendId, MyProc->vxid.lxid,
+			 MyProc->vxid.procNumber, MyProc->vxid.lxid,
 			 list_length(exportedSnapshots) + 1);
 
 	/*
@@ -1182,7 +1182,7 @@ ExportSnapshot(Snapshot snapshot)
 	 */
 	initStringInfo(&buf);
 
-	appendStringInfo(&buf, "vxid:%d/%u\n", MyProc->vxid.backendId, MyProc->vxid.lxid);
+	appendStringInfo(&buf, "vxid:%d/%u\n", MyProc->vxid.procNumber, MyProc->vxid.lxid);
 	appendStringInfo(&buf, "pid:%d\n", MyProcPid);
 	appendStringInfo(&buf, "dbid:%u\n", MyDatabaseId);
 	appendStringInfo(&buf, "iso:%d\n", XactIsoLevel);
@@ -1352,7 +1352,7 @@ parseVxidFromText(const char *prefix, char **s, const char *filename,
 				(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
 				 errmsg("invalid snapshot data in file \"%s\"", filename)));
 	ptr += prefixlen;
-	if (sscanf(ptr, "%d/%u", &vxid->backendId, &vxid->localTransactionId) != 2)
+	if (sscanf(ptr, "%d/%u", &vxid->procNumber, &vxid->localTransactionId) != 2)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
 				 errmsg("invalid snapshot data in file \"%s\"", filename)));