Thanks, I know about alerts.
I don't need collections for this database because it takes space.
Eg, SQL Monitor works since 3 April 2014. Table data.Cluster_SqlServer_Database_Performance_UnstableSamples has about 58 000 000 records of which 48 000 000 records related to readonly databases for one server. And so on for tables Cluster_SqlServer_Database_Perfomance_... And imagine that we have few servers with about 100 readonly databases.
I want reduce RedGateMonitor database size but I dont want purge data for normal databases. So if I cant do this by in SQL Monitor I will have to do with handmade purge