row0mysql.c, row0ins.c:

  Fix bug #5961: release the dictionary latch during a long cascaded FOREIGN KEY operation, so that we do not starve other users

innobase/row/row0ins.c

@@ -966,6 +966,23 @@ row_ins_foreign_check_on_constraint(
 	
 	err = row_update_cascade_for_mysql(thr, cascade,
 						foreign->foreign_table);
+
+	if (foreign->foreign_table->n_foreign_key_checks_running == 0) {
+		fprintf(stderr,
+"InnoDB: error: table %s has the counter 0 though there is\n"
+"InnoDB: a FOREIGN KEY check running on it.\n",
+			foreign->foreign_table->name);
+	}
+
+	/* Release the data dictionary latch for a while, so that we do not
+	starve other threads from doing CREATE TABLE etc. if we have a huge
+	cascaded operation running. The counter n_foreign_key_checks_running
+	will prevent other users from dropping or ALTERing the table when we
+	release the latch. */
+
+	row_mysql_unfreeze_data_dictionary(thr_get_trx(thr));
+	row_mysql_freeze_data_dictionary(thr_get_trx(thr));
+
 	mtr_start(mtr);
 
 	/* Restore pcur position */

innobase/row/row0mysql.c

@@ -2156,8 +2156,8 @@ row_drop_table_for_mysql(
 		fputs("	 InnoDB: You are trying to drop table ", stderr);
 		ut_print_name(stderr, table->name);
 		fputs("\n"
-		  "InnoDB: though there are foreign key check running on it.\n"
-		  "InnoDB: Adding the table to the background drop queue.\n",
+		 "InnoDB: though there is a foreign key check running on it.\n"
+		 "InnoDB: Adding the table to the background drop queue.\n",
 			stderr);
 
 		row_add_table_to_background_drop_list(table);