private void scheduleDetermineMaxActiveSessionsTask() {
    TimerTask task = new TimerTask() {
      @Override
      public void run() {
        int currentActiveSessions = 0;
        try {
          currentActiveSessions = getSessionCache().size();
        } catch (Exception ignore) {
        }
        if (currentActiveSessions > getMaxActive()) {
          setMaxActive(currentActiveSessions);
          if (getLogger().isDebugEnabled()) {
            getLogger().debug(
                DeltaSessionManager.this + ": Set max active sessions: " + currentActiveSessions);
          }
        }
      }
    };

    timer.schedule(task, TIMER_TASK_DELAY, TIMER_TASK_PERIOD);
  }
For debugging: return a list of all session ids currently active
extensions/geode-modules/src/main/java/org/apache/geode/modules/session/catalina/DeltaSessionManager.java