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

1 files changed, 7 insertions, 6 deletions

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);