4 files changed, 79 insertions, 14 deletions

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 0ae07227941..4aff6cf7f27 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -471,6 +471,7 @@ MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid, const char *gid,
 	proc->backendId = InvalidBackendId;
 	proc->databaseId = databaseid;
 	proc->roleId = owner;
+	proc->tempNamespaceId = InvalidOid;
 	proc->isBackgroundWorker = false;
 	proc->lwWaiting = false;
 	proc->lwWaitMode = 0;
diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index 0f67a122ede..3971346e738 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"
@@ -3205,6 +3205,46 @@ isOtherTempNamespace(Oid namespaceId)
 }
 
 /*
+ * isTempNamespaceInUse - is the given namespace owned and actively used
+ * by a backend?
+ *
+ * Note: this can be used while scanning relations in pg_class to detect
+ * orphaned temporary tables or namespaces with a backend connected to a
+ * given database.  The result may be out of date quickly, so the caller
+ * must be careful how to handle this information.
+ */
+bool
+isTempNamespaceInUse(Oid namespaceId)
+{
+	PGPROC	   *proc;
+	int			backendId;
+
+	Assert(OidIsValid(MyDatabaseId));
+
+	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 same database we are looking at? */
+	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
  * that owns it.  Temporary-toast-table namespaces are included, too.
@@ -3893,6 +3933,16 @@ InitTempTableNamespace(void)
 	myTempNamespace = namespaceId;
 	myTempToastNamespace = toastspaceId;
 
+	/*
+	 * Mark MyProc as owning this namespace which other processes can use to
+	 * decide if a temporary namespace is in use or not.  We assume that
+	 * assignment of namespaceId is an atomic operation.  Even if it is not,
+	 * the temporary relation which resulted in the creation of this temporary
+	 * namespace is still locked until the current transaction commits, so it
+	 * would not be accessible yet, acting as a barrier.
+	 */
+	MyProc->tempNamespaceId = namespaceId;
+
 	/* It should not be done already. */
 	AssertState(myTempNamespaceSubID == InvalidSubTransactionId);
 	myTempNamespaceSubID = GetCurrentSubTransactionId();
@@ -3923,6 +3973,15 @@ AtEOXact_Namespace(bool isCommit, bool parallel)
 			myTempNamespace = InvalidOid;
 			myTempToastNamespace = InvalidOid;
 			baseSearchPathValid = false;	/* need to rebuild list */
+
+			/*
+			 * Reset the temporary namespace flag in MyProc.  We assume that
+			 * this operation is atomic.  Even if it is not, the temporary
+			 * table which created this namespace is still locked until this
+			 * transaction aborts so it would not be visible yet, acting as a
+			 * barrier.
+			 */
+			MyProc->tempNamespaceId = InvalidOid;
 		}
 		myTempNamespaceSubID = InvalidSubTransactionId;
 	}
@@ -3975,6 +4034,15 @@ AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
 			myTempNamespace = InvalidOid;
 			myTempToastNamespace = InvalidOid;
 			baseSearchPathValid = false;	/* need to rebuild list */
+
+			/*
+			 * Reset the temporary namespace flag in MyProc.  We assume that
+			 * this operation is atomic.  Even if it is not, the temporary
+			 * table which created this namespace is still locked until this
+			 * transaction aborts so it would not be visible yet, acting as a
+			 * barrier.
+			 */
+			MyProc->tempNamespaceId = InvalidOid;
 		}
 	}
 
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 1d9cfc63d22..978089575b8 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
@@ -2215,7 +2212,6 @@ do_autovacuum(void)
 	{
 		Oid			relid = lfirst_oid(cell);
 		Form_pg_class classForm;
-		int			backendID;
 		ObjectAddress object;
 
 		/*
@@ -2257,10 +2253,8 @@ 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 6f30e082b26..6f9aaa52faf 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;