reset_temp_schema_v3.patch

diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index 0f67a122ed..0630032148 100644
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -47,7 +47,7 @@
 #include "parser/parse_func.h"
 #include "storage/ipc.h"
 #include "storage/lmgr.h"
-#include "storage/sinval.h"
+#include "storage/sinvaladt.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/catcache.h"
@@ -3204,6 +3204,42 @@ isOtherTempNamespace(Oid namespaceId)
 	return isAnyTempNamespace(namespaceId);
 }
 
+/*
+ * isTempNamespaceInUse - is the given namespace owned and actively used
+ * by a backend?
+ *
+ * Note: this is used by autovacuum to detect the presence of orphaned
+ * temporary tables, based on the active namespace tracked by PGPROC entries.
+ */
+bool
+isTempNamespaceInUse(Oid namespaceId)
+{
+	PGPROC	   *proc;
+	int			backendId;
+
+	backendId = GetTempNamespaceBackendId(namespaceId);
+
+	if (backendId == InvalidBackendId ||
+		backendId == MyBackendId)
+		return false;
+
+	/* Is the backend alive? */
+	proc = BackendIdGetProc(backendId);
+	if (proc == NULL)
+		return false;
+
+	/* Is the backend connected to the database being vacuumed? */
+	if (proc->databaseId != MyDatabaseId)
+		return false;
+
+	/* Does the backend own the temporary namespace? */
+	if (proc->tempNamespaceId != namespaceId)
+		return false;
+
+	/* all good to go */
+	return true;
+}
+
 /*
  * GetTempNamespaceBackendId - if the given namespace is a temporary-table
  * namespace (either my own, or another backend's), return the BackendId
@@ -3893,6 +3929,15 @@ InitTempTableNamespace(void)
 	myTempNamespace = namespaceId;
 	myTempToastNamespace = toastspaceId;
 
+	/*
+	 * Mark the proc entry as owning this namespace which autovacuum uses to
+	 * decide if a temporary file entry can be marked as orphaned or not. Even
+	 * if this is an atomic operation, this can be safely done lock-less as no
+	 * temporary relations associated to it can be seen yet by autovacuum when
+	 * scanning pg_class.
+	 */
+	MyProc->tempNamespaceId = namespaceId;
+
 	/* It should not be done already. */
 	AssertState(myTempNamespaceSubID == InvalidSubTransactionId);
 	myTempNamespaceSubID = GetCurrentSubTransactionId();
@@ -3923,6 +3968,14 @@ AtEOXact_Namespace(bool isCommit, bool parallel)
 			myTempNamespace = InvalidOid;
 			myTempToastNamespace = InvalidOid;
 			baseSearchPathValid = false;	/* need to rebuild list */
+
+			/*
+			 * Reset the temporary namespace flag in the proc entry. The
+			 * creation of the temporary namespace has failed for some reason
+			 * and cannot be seen by autovacuum as it has not been committed,
+			 * hence it is fine to do this in a lock-less fashion.
+			 */
+			MyProc->tempNamespaceId = InvalidOid;
 		}
 		myTempNamespaceSubID = InvalidSubTransactionId;
 	}
@@ -3975,6 +4028,14 @@ AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
 			myTempNamespace = InvalidOid;
 			myTempToastNamespace = InvalidOid;
 			baseSearchPathValid = false;	/* need to rebuild list */
+
+			/*
+			 * Reset the temporary namespace flag in the proc entry. The
+			 * creation of the temporary namespace has failed for some reason
+			 * and cannot be seen by autovacuum as it has not been committed,
+			 * hence it is fine to do this in a lock-less fashion.
+			 */
+			MyProc->tempNamespaceId = InvalidOid;
 		}
 	}
 
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 1d9cfc63d2..9f45ffcea3 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2080,14 +2080,11 @@ do_autovacuum(void)
 		 */
 		if (classForm->relpersistence == RELPERSISTENCE_TEMP)
 		{
-			int			backendID;
-
-			backendID = GetTempNamespaceBackendId(classForm->relnamespace);
-
-			/* We just ignore it if the owning backend is still active */
-			if (backendID != InvalidBackendId &&
-				(backendID == MyBackendId ||
-				 BackendIdGetProc(backendID) == NULL))
+			/*
+			 * We just ignore it if the owning backend is still active and
+			 * using the temporary schema.
+			 */
+			if (!isTempNamespaceInUse(classForm->relnamespace))
 			{
 				/*
 				 * The table seems to be orphaned -- although it might be that
@@ -2257,10 +2254,8 @@ do_autovacuum(void)
 			UnlockRelationOid(relid, AccessExclusiveLock);
 			continue;
 		}
-		backendID = GetTempNamespaceBackendId(classForm->relnamespace);
-		if (!(backendID != InvalidBackendId &&
-			  (backendID == MyBackendId ||
-			   BackendIdGetProc(backendID) == NULL)))
+
+		if (isTempNamespaceInUse(classForm->relnamespace))
 		{
 			UnlockRelationOid(relid, AccessExclusiveLock);
 			continue;
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 6f30e082b2..6f9aaa52fa 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -371,6 +371,7 @@ InitProcess(void)
 	MyProc->backendId = InvalidBackendId;
 	MyProc->databaseId = InvalidOid;
 	MyProc->roleId = InvalidOid;
+	MyProc->tempNamespaceId = InvalidOid;
 	MyProc->isBackgroundWorker = IsBackgroundWorker;
 	MyPgXact->delayChkpt = false;
 	MyPgXact->vacuumFlags = 0;
@@ -552,6 +553,7 @@ InitAuxiliaryProcess(void)
 	MyProc->backendId = InvalidBackendId;
 	MyProc->databaseId = InvalidOid;
 	MyProc->roleId = InvalidOid;
+	MyProc->tempNamespaceId = InvalidOid;
 	MyProc->isBackgroundWorker = IsBackgroundWorker;
 	MyPgXact->delayChkpt = false;
 	MyPgXact->vacuumFlags = 0;
diff --git a/src/include/catalog/namespace.h b/src/include/catalog/namespace.h
index 7991de5e21..0e202372d5 100644
--- a/src/include/catalog/namespace.h
+++ b/src/include/catalog/namespace.h
@@ -137,6 +137,7 @@ extern bool isTempToastNamespace(Oid namespaceId);
 extern bool isTempOrTempToastNamespace(Oid namespaceId);
 extern bool isAnyTempNamespace(Oid namespaceId);
 extern bool isOtherTempNamespace(Oid namespaceId);
+extern bool isTempNamespaceInUse(Oid namespaceId);
 extern int	GetTempNamespaceBackendId(Oid namespaceId);
 extern Oid	GetTempToastNamespace(void);
 extern void GetTempNamespaceState(Oid *tempNamespaceId,
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 5c19a61dcf..cb613c8076 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -114,6 +114,9 @@ struct PGPROC
 	Oid			databaseId;		/* OID of database this backend is using */
 	Oid			roleId;			/* OID of role using this backend */
 
+	Oid			tempNamespaceId;	/* OID of temp schema this backend is
+									 * using */
+
 	bool		isBackgroundWorker; /* true if background worker. */
 
 	/*