You can configure audit history purging and archiving in BES Admin.
You can have BigFix on a schedule write out the audit history to a file, then delete the history that is older than X days from the server. This way you can always have X days of audit history “live” within the root server database, but also retain an audit history archive for long term keeping. This is highly recommended to enable for large environments with large numbers of endpoints and actions, and just a good idea for performance in general.
Having at least 3 months of live audit history is ideal, but some very large environments reduce it to a week for performance reasons.
BES Admin Info: https://help.hcltechsw.com/bigfix/9.5/platform/Platform/Installation/c_running_the_tivoli_endpoint_ma.html