There are options available within Spotlight to restrict the amount of data retained by the Predictive Diagnostics module objects.
1. In Spotlight connect to Oracle instance containing QUEST_PPCM tables.
2. Select View | Option menu option.
3. Go under Predictive Diagnostics section and select Impending Bottlenecks Oracle option.
4. For each three fields here, reduce the Data Retention Period.
**Note less data means PPCM will obviously have less data to use for predictions but this will keep table sto smaller size.
These changes will automatically shrink the size of these tables.