What causes an ORA-12519 to be thrown even though the Oracle trace file for the event shows an ORA-00020?

Question

When we are connecting to Oracle via the listener and we reach our process limit, we're getting an ORA-12519: TNS:no appropriate service handler found. Looking at the the trace file for the event, it's showing an ORA-00020: maximum number of processes (%s) exceeded [where %s is our process limit of course].

What would cause Oracle to throw the misleading error message instead of the one for the real problem?

(I would have added a tag for ora-00020 but I don't have enough rep to add a new one.)

Answer 1

ORA-00020 is a database error. ORA-12519 is a TNS error.

Since you are using directly TNS (and database only indirectly), you directly get TNS error (and indirectly database error). As much as TNS is involved, there is no appropriate handler, and this is caused by the underlying database error.