After upgrading our databases to 12.2, we found that an extremely large number of trace files were generated. After a closer analysis we found that every 3 seconds an MMON trace file with the following content was generated.
AUTO SGA: kmgs_parameter_update_timeout gen0 0 mmon alive 1
The reason for this is that a developer has unfortunately forgotten to deactivate a trace event, so that it is automatically activated for every 12.2 database after the upgrade. It is not possible to correct this with a parameter, but there is a patch that deactivates the tracing.
The details are described under the following note
In the note is written that this problem is fixed with the January 2018 release update, but this is unfortunately not true. Even with the current April 2018 release update, the patch is still necessary!
If you notice an extreme increase in your trace directories after the upgrade, this could be the reason why