InterSystems FAQ rubric
For volatile tables (tables with many INSERTs and DELETEs), storage for bitmap indexes can become inefficient over time.
For example, suppose that there are thousands of data with the following definition, and the operation of bulk deletion with TRUNCATE TABLE after being retained for a certain period of time is repeatedly performed.
Class MyWork.MonthData Extends (%Persistent, %Populate)
{
/// Level of satisfaction
Property Satisfaction As %String(VALUELIST = ",満足,やや満足,やや不満,不満,");
/// Age
Property Age As %Integer(MAXVAL = 70, MINVAL = 20);
Index AgeIdx On Age [ Type = bitmap ];
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