We have a Purge by Date function, where we query JBPM_PROCESSINSTANCE for instances that have ended before a given retention date, and then delete the process instances returned by that query.

We also modified jBPM's logging to restrict the type of log records that get generated (JBPM_LOG is the biggest disk hog of the bunch). For example, turning off variable update logging reduces the log table size and activity by about 50 percent.

in jbpm4 the DbSessionImpl has a deleteProcessDefinitionHistory() method, you can use that as base for whatever history information you want to delete:

   List<HistoryProcessInstanceImpl> historyProcessInstances = session
            .createCriteria(HistoryProcessInstanceImpl.class)
            .add(Restrictions.eq("processDefinitionId", processDefinitionId))

            .add(... insert random other Restriction here ...)

            .list();

    // you also have to delete the activity since they have a foreign key relationship

    for (HistoryProcessInstanceImpl hpi : historyProcessInstances) {
      List<HistoryActivityInstanceImpl> historyActivityInstances = session
              .createCriteria(HistoryActivityInstanceImpl.class)
              .add(Restrictions.eq("historyProcessInstance", hpi))
              .list();
      for (HistoryActivityInstanceImpl hai : historyActivityInstances) {
        session.delete(hai);
      }
      session.delete(hpi);
    }