JDBC ORA-12850
Some developers report ORA-12850 error in their JDBC log.
ORA-12850: Could not allocate slaves on all specified instances: 2 needed, 0 allocated
There could be many ways to solve this, but I run the following statement to remove ORA-12850.
SQL> alter system flush shared_pool;
System altered.
For a RAC system, you should flush shared pool on other nodes, too.
In this way, we don't have to restart the database.
Toad ORA-12850
Met an error when I tried to monitor the database by querying sessions in Toad for Oracle.

ORA-12850
To work around the error, we should prevent Toad to allocate slave processes on other node in this moment, you can uncheck "Use RAC Views" like this.

Toad - Session Browser - Uncheck "Use RAC Views"