Toad for Oracle Editor – How do I debug PL/SQL when connected to a RAC?

The DBMS Debugger debugs PL/SQL.

Using the Debugger, you can set breakpoints, watches, and see call stacks. In addition, you can view DBMS output.

Note: When using the PL/SQL Debugger and connecting to a RAC instance, you must have the TNSNAMES entry for the instance with the server directed the use connection or session here. Or, you must connect directly to an instance of the cluster without letting the server assign an instance. 

Regarding earlier versions of Toad:  When using the PL/SQLDebugger with a RAC database, you must either have an additional entry in your TNSNames.ora file for the connected instance, or you must connect directly to an instance of the cluster without letting the server assign an instance.

During debugging, Toad creates two background sessions for handling debugger calls, called the Target and Debug sessions. These two sessions must be created on the same instance as the main Toad session, because Oracle does not support Debugging across RAC instances.

To accomplish this, Toad queries the data dictionary to find the current instance name, then searches the TNSNames.ora file, starting at the beginning, for the first entry which has either the SERVICE_NAME or INSTANCE_NAME equal to the name found in the data dictionary. Toad will then use this secondary TNSNames entry when creating the background debugger sessions.

For example, in a two node RAC environment, a user would have their main RAC entry looking something like this:

RAC =
  (DESCRIPTION =
      (ADDRESS_LIST =
          (ADDRESS = (PROTOCOL = TCP)(HOST = 192.0.0.1)(PORT = 1521))
          (ADDRESS = (PROTOCOL = TCP)(HOST = 192.0.0.2)(PORT = 1521))            
      )
      (LOAD_BALANCE = ON)
      (CONNECT_DATA =
          (SERVICE_NAME = RAC)
          (FAILOVER_MODE = 
      (TYPE = SELECT)
      (METHOD = BASIC)
      (RETRIES = 180)
            (DELAY = 5)
          )
      )
  )

In this two node environment, the user would then need to have two additional TNSNames entries, one each for the individual instances in the RAC. In these entries, the can either use the syntax: 

RAC1 =
  (DESCRIPTION =
      (ADDRESS_LIST =
          (ADDRESS = (PROTOCOL = TCP)(HOST = 192.0.0.1)(PORT = 1521))
      )
      (CONNECT_DATA =
          (SERVICE_NAME = RAC)       # notice the difference
          (INSTANCE_NAME = RAC1)     # betwen this
      )
  )

Or: 

RAC2 =
  (DESCRIPTION =
      (ADDRESS_LIST =
          (ADDRESS = (PROTOCOL = TCP)(HOST = 192.0.0.2)(PORT = 1521))
      )
      (CONNECT_DATA =
          (SERVICE_NAME = RAC2)      # and this
      )
  )