Increase batch size.

src/Commands/DrushCommands.php

@@ -40,6 +40,8 @@ class DrushCommands extends BaseDrushCommands {
         '@count' => $count_users_not_migrated,
         '@ids' => $user_ids_as_string,
       ]));
+
+      // @todo do something about it.
     }
   }
 
@@ -99,8 +101,8 @@ class DrushCommands extends BaseDrushCommands {
    */
   protected function usersFromDatabaseANotInDatabaseB($database_a, $database_b) {
     $count_users = $this->getUserCounts($database_a);
-    // Memory usage around 30MB for 20000.
-    $length = 20000;
+    // Memory usage around 40MB for 30000.
+    $length = 30000;
     $offset = 0;
     $extra_users = [];