Issue:
Trimming and shrinking ION_Data database as the need will arise

Environment:
ION_Data as installed with PME (formerly ION Enterprise, SMS)

Cause and Resolution:
When data is added to the database, new rows are created which contain all the data. When database is trimmed, data from all the rows that lie within the time frame specified for trimming is removed. But those rows are left there. They are empty and cannot be used again to fill with data.

This is where shrinking comes in. It deletes those empty rows left out after trimming. So you free up some actual space only after shrinking and not just after trimming. Keep in mind, one can shrink only after trimming because shrinking will remove only empty rows and trimming will delete data from rows and make them empty.

A scheduled maintenance plan is automatically created and enabled for the ION_Data database which takes care of shrinking and some other tasks. But since a trim task is not enabled by default, shrinking doesn't impact anything until trimming removes data from rows.

When you want to shrink a database, the box that opens shows allocated space in a database and free space. When you click OK, the free space is subtracted from allocated space and that is the remaining database space. Here the free space means empty rows left out by trimming which are empty but still cannot accept any new data.