ORA-00093: pga_aggregate_limit must be between...

Starting 18c, pga_aggregate_limit setting has also been made dependent on PROCESSES initialization parameter. You might face ORA-00093 during startup of instance if value of pga_aggregate_limit is below the required value. For my 19c instance I faced same issue as follows.

SQL> startup nomount ORA-00093: pga_aggregate_limit must be between 45000M and 100000G ORA-01078: failure in processing system parameters SQL>

 As per above example, pga_aggregate_limit must have been set to at least 45000M after I set PROCESSES parameter’s value to 9000. As per documentation, the value of pga_aggregate_limit should be 3MB multiplied by the value of PROCESSES parameter for single instance database and at least 5MB multiplied by the value set for PROCESS parameter if this is a RAC database. For 18c, 3M multiplied by value or PROCESS would suffice in both cases of single instance or RAC. This means that if we set PROCESSES parameter value to 10000, the value of pga_aggregate_limit parameter should be at least 30000M (10000*3) for single instance database, or 50000M (10000*5) for a RAC database instance.