The meaning of the HistoryRetentionLimit depends on the setting of the HistoryRetentionOptions: 

• If HistoryRetentionOptions=HistoryRetentionOptionsEnum.hrRetainXDays, the HistoryRetentionLimit specifies the number of days for which the history should be retained. Any ExecutionHistoryItems or LogEvents for the job that are older than this number of days will be purged.

• If HistoryRetentionOptions=HistoryRetentionOptionsEnum.hrRetainXEcecutions, the HistoryRetentionLimit specifies the number of instances that should be retained. If HistoryRetentionLimit=n, then any instances other than the most recent n instances will be purged.

For all other settings, the HistoryRetentionLimit is ignored.

In some cases the retention limit may be overridden by the server. For example, if the server is using an MSDE database, there is a limit to the amount of data the database will allow. To prevent this limit from being exceeded, adTempus limits retention to 200 instances per job. Additionally, if the database size approaches the database size limit, adTempus may automatically purge additional history records.