As described in What are cardinality statistics?, the cardinality statistics for a table influence the optimizer's choice of a query plan for a query which accesses the table's data. If the cardinality statistics are missing or out of date, the optimizer may choose an inferior query plan, resulting in poor performance.
One common situation which can causing missing or out of date statistics is when indexes are created before the data is added to the tables. Cardinality statistics are automatically updated in certain situations, such as when an index is added to an existing non-empty table. When cardinality statistics are automatically updated describes the automatic statistics updates in more detail. However, adding, updating, and deleting data after the index has been created can cause the cardinality statistics to become stale; see when cardinality statistics go stale for more information about what can cause missing or out of date statistics..
You can find additional information about these system procedures, including the syntax for invoking them, in the Java DB Reference Manual.