default_route_behaviour: BLOCK

[Denchick]

If the default_route_behaviour is set to BLOCK, the router will send a message to the client:

ERROR:  client processing error: error processing query 'CREATE TABLE test_pers (puid INT, data JSONB);': failed to match any datashard., tx status IDLE

This message can be misleading for users, so it would be better if the router could answer with a more informative message, such as "Your query is blocked due to the default route behavior."