The Dispatchers Busy alarm occurs when all or most dispatcher processes are busy.
In an MTS environment, multiple sessions share a smaller number of shared server processes. These processes perform database activities on their behalf. The servers are usually allocated by a smaller number of dispatcher processes.
The number of dispatchers can increase up to the limits set by the configuration parameter MAX_DISPATCHERS. If the demand for the processes causes all servers to become busy, sessions may experience long wait times before a server becomes available.
See the Activity | Server Page to obtain the precise load on dispatchers. If sessions are waiting on it, either increase the number of dispatchers or use dedicated server processes.