This depend on how often is runned procedure that purge scheduler log.
There is a procedure dbms_scheduler.purge_log that is runnem by job PURGE_LOG. Job is owner by SYS.
By default, the Scheduler automatically purges all rows in the job log and window log that are older than 30 days.
You can check you setting by this
DECLARE v VARCHAR2(1000); BEGIN dbms_scheduler.get_scheduler_attribute('LOG_HISTORY',v); dbms_output.put_line(v); END; /
to change setting use
BEGIN dbms_scheduler.set_scheduler_attribute('LOG_HISTORY',90); END; /
This example set log_history attribute to 90 days. So only record older than 90 days will be erased.