Report Server uses Report Server Temporary database to store session and execution data, information related to cached reports. These tables in the ReporServerTemp database hold temporary data and there are certain Stored Procedures which periodically remove older data from the ReportServerTemp database.
Therefore, ReportServerTemp database only being a scratchpad holding temporary data for a limited period of time it is recommended that we have the Recovery Model for the ReportServerTemp database set to Simple. By default, the Recovery Model for ReportServerTemp database is set to Simple.
When we configure Reporting Services to work with Always On