diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 59ca5cd5a9..f7202cc9e7 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -717,9 +717,21 @@ execute_sql_string(const char *sql)
 	foreach(lc1, raw_parsetree_list)
 	{
 		RawStmt    *parsetree = lfirst_node(RawStmt, lc1);
+		MemoryContext per_parsetree_context,
+					oldcontext;
 		List	   *stmt_list;
 		ListCell   *lc2;
 
+		/*
+		 * We do the work for each parsetree in a short-lived context, to
+		 * limit the memory used when there are many commands in the string.
+		 */
+		per_parsetree_context =
+			AllocSetContextCreate(CurrentMemoryContext,
+								  "execute_sql_string per-statement context",
+								  ALLOCSET_DEFAULT_SIZES);
+		oldcontext = MemoryContextSwitchTo(per_parsetree_context);
+
 		/* Be sure parser can see any DDL done so far */
 		CommandCounterIncrement();
 
@@ -772,6 +784,10 @@ execute_sql_string(const char *sql)
 
 			PopActiveSnapshot();
 		}
+
+		/* Clean up per-parsetree context. */
+		MemoryContextSwitchTo(oldcontext);
+		MemoryContextDelete(per_parsetree_context);
 	}
 
 	/* Be sure to advance the command counter after the last script command */
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 44a59e1d4f..ffd84d877c 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -1070,6 +1070,7 @@ exec_simple_query(const char *query_string)
 		bool		snapshot_set = false;
 		const char *commandTag;
 		char		completionTag[COMPLETION_TAG_BUFSIZE];
+		MemoryContext per_parsetree_context = NULL;
 		List	   *querytree_list,
 				   *plantree_list;
 		Portal		portal;
@@ -1132,10 +1133,25 @@ exec_simple_query(const char *query_string)
 		/*
 		 * OK to analyze, rewrite, and plan this query.
 		 *
-		 * Switch to appropriate context for constructing querytrees (again,
-		 * these must outlive the execution context).
+		 * Switch to appropriate context for constructing query and plan trees
+		 * (these can't be in the transaction context, as that will get reset
+		 * when the command is COMMIT/ROLLBACK).  If we have multiple
+		 * parsetrees, we use a separate context for each one, so that we can
+		 * free that memory before moving on to the next one.  But for the
+		 * last (or only) parsetree, just use MessageContext, which will be
+		 * reset shortly after completion anyway.  In event of an error, the
+		 * per_parsetree_context will be deleted when MessageContext is reset.
 		 */
-		oldcontext = MemoryContextSwitchTo(MessageContext);
+		if (lnext(parsetree_item) != NULL)
+		{
+			per_parsetree_context =
+				AllocSetContextCreate(MessageContext,
+									  "per-parsetree message context",
+									  ALLOCSET_DEFAULT_SIZES);
+			oldcontext = MemoryContextSwitchTo(per_parsetree_context);
+		}
+		else
+			oldcontext = MemoryContextSwitchTo(MessageContext);
 
 		querytree_list = pg_analyze_and_rewrite(parsetree, query_string,
 												NULL, 0, NULL);
@@ -1160,8 +1176,8 @@ exec_simple_query(const char *query_string)
 
 		/*
 		 * We don't have to copy anything into the portal, because everything
-		 * we are passing here is in MessageContext, which will outlive the
-		 * portal anyway.
+		 * we are passing here is in MessageContext or the
+		 * per_parsetree_context, and so will outlive the portal anyway.
 		 */
 		PortalDefineQuery(portal,
 						  NULL,
@@ -1263,6 +1279,10 @@ exec_simple_query(const char *query_string)
 		 * aborted by error will not send an EndCommand report at all.)
 		 */
 		EndCommand(completionTag, dest);
+
+		/* Now we may drop the per-parsetree context, if one was created. */
+		if (per_parsetree_context)
+			MemoryContextDelete(per_parsetree_context);
 	}							/* end loop over parsetrees */
 
 	/*