Avoid re-assigning the global pid for client backends and bg workers when the application_name changes

src/backend/distributed/metadata/metadata_cache.c

@@ -4545,6 +4545,16 @@ GetLocalNodeId(void)
 }
 
 
+/*
+ * CachedLocalNodeIdIsValid return true if the cached local node id is valid.
+ */
+bool
+CachedLocalNodeIdIsValid(void)
+{
+	return LocalNodeId != -1;
+}
+
+
 /*
  * RegisterLocalGroupIdCacheCallbacks registers the callbacks required to
  * maintain LocalGroupId at a consistent value. It's separate from

src/backend/distributed/shared_library_init.c

@@ -2899,6 +2899,13 @@ ApplicationNameAssignHook(const char *newval, void *extra)
 	 * So we set the FinishedStartupCitusBackend flag in StartupCitusBackend to
 	 * indicate when this responsibility handoff has happened.
 	 *
+	 * On the other hand, even if now it's this hook's responsibility to update
+	 * the global pid, we cannot do so if the cached local node id is invalidated
+	 * and we're not allowed to access the catalog tables. Within a transaction
+	 * block, we can access the catalog tables. For this reason, in addition to
+	 * checking FinishedStartupCitusBackend, we also require either being in a
+	 * transaction block or the cached local node id to be valid.
+	 *
 	 * Another solution to the catalog table acccess problem would be to update
 	 * global pid lazily, like we do for HideShards. But that's not possible
 	 * for the global pid, since it is stored in shared memory instead of in a
@@ -2907,7 +2914,8 @@ ApplicationNameAssignHook(const char *newval, void *extra)
 	 * as reasonably possible, which is also why we extract global pids in the
 	 * AuthHook already (extracting doesn't require catalog access).
 	 */
-	if (FinishedStartupCitusBackend)
+	if (FinishedStartupCitusBackend &&
+		(IsTransactionState() || CachedLocalNodeIdIsValid()))
 	{
 		AssignGlobalPID(newval);
 	}

src/include/distributed/metadata_cache.h

@@ -181,6 +181,7 @@ extern CitusTableCacheEntry * LookupCitusTableCacheEntry(Oid relationId);
 extern DistObjectCacheEntry * LookupDistObjectCacheEntry(Oid classid, Oid objid, int32
 														 objsubid);
 extern int32 GetLocalGroupId(void);
+extern bool CachedLocalNodeIdIsValid(void);
 extern int32 GetLocalNodeId(void);
 extern void CitusTableCacheFlushInvalidatedEntries(void);
 extern Oid LookupShardRelationFromCatalog(int64 shardId, bool missing_ok);