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

2 files changed, 17 insertions, 17 deletions

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: