fix-bug-18545-wip.patch

diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index 8613fc6fb5..06331d906a 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -1410,10 +1410,6 @@ ParallelWorkerMain(Datum main_arg)
 	libraryspace = shm_toc_lookup(toc, PARALLEL_KEY_LIBRARY, false);
 	StartTransactionCommand();
 	RestoreLibraryState(libraryspace);
-
-	/* Restore GUC values from launching backend. */
-	gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC, false);
-	RestoreGUCState(gucspace);
 	CommitTransactionCommand();
 
 	/* Crank up a transaction state appropriate to a parallel worker. */
@@ -1455,6 +1451,14 @@ ParallelWorkerMain(Datum main_arg)
 	 */
 	InvalidateSystemCaches();
 
+	/*
+	 * Restore GUC values from launching backend.  We can't do this earlier,
+	 * because GUCs that do catalog lookups (such as session_authorization)
+	 * need to see the same database state as the leader.
+	 */
+	gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC, false);
+	RestoreGUCState(gucspace);
+
 	/*
 	 * Restore current role id.  Skip verifying whether session user is
 	 * allowed to become this role and blindly restore the leader's state for
diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index 9345131711..b2a00ae0f0 100644
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -577,14 +577,16 @@ check_transaction_read_only(bool *newval, void **extra, GucSource source)
  * We allow idempotent changes at any time, but otherwise this can only be
  * changed in a toplevel transaction that has not yet taken a snapshot.
  *
- * As in check_transaction_read_only, allow it if not inside a transaction.
+ * As in check_transaction_read_only, allow it if not inside a transaction,
+ * or if restoring state in a parallel worker.
  */
 bool
 check_transaction_isolation(int *newval, void **extra, GucSource source)
 {
 	int			newXactIsoLevel = *newval;
 
-	if (newXactIsoLevel != XactIsoLevel && IsTransactionState())
+	if (newXactIsoLevel != XactIsoLevel &&
+		IsTransactionState() && !InitializingParallelWorker)
 	{
 		if (FirstSnapshotSet)
 		{
@@ -619,6 +621,10 @@ check_transaction_isolation(int *newval, void **extra, GucSource source)
 bool
 check_transaction_deferrable(bool *newval, void **extra, GucSource source)
 {
+	/* Just accept the value when restoring state in a parallel worker */
+	if (InitializingParallelWorker)
+		return true;
+
 	if (IsSubTransaction())
 	{
 		GUC_check_errcode(ERRCODE_ACTIVE_SQL_TRANSACTION);
@@ -811,6 +817,15 @@ check_session_authorization(char **newval, void **extra, GucSource source)
 	if (*newval == NULL)
 		return true;
 
+	/*
+	 * Do nothing if initializing a parallel worker: ParallelWorkerMain is
+	 * responsible for setting the active role.  We just need to absorb the
+	 * leader's value of session_authorization in case some user code looks at
+	 * it.
+	 */
+	if (InitializingParallelWorker)
+		return true;
+
 	if (!IsTransactionState())
 	{
 		/*
@@ -886,7 +901,7 @@ assign_session_authorization(const char *newval, void *extra)
 {
 	role_auth_extra *myextra = (role_auth_extra *) extra;
 
-	/* Do nothing for the boot_val default of NULL */
+	/* Do nothing for the boot_val default of NULL, and in parallel workers */
 	if (!myextra)
 		return;