/** Invoked after a non-sticky session is removed from memcached. */
  protected void onAfterDeleteFromMemcached(@Nonnull final String sessionId) {
    final long start = System.currentTimeMillis();

    final String validityInfoKey = _sessionIdFormat.createValidityInfoKeyName(sessionId);
    _memcached.delete(validityInfoKey);

    if (_storeSecondaryBackup) {
      _memcached.delete(_sessionIdFormat.createBackupKey(sessionId));
      _memcached.delete(_sessionIdFormat.createBackupKey(validityInfoKey));
    }

    _stats.registerSince(NON_STICKY_AFTER_DELETE_FROM_MEMCACHED, start);
  }
 @CheckForNull
 protected SessionValidityInfo loadBackupSessionValidityInfo(@Nonnull final String sessionId) {
   final String key = _sessionIdFormat.createValidityInfoKeyName(sessionId);
   final String backupKey = _sessionIdFormat.createBackupKey(key);
   return loadSessionValidityInfoForValidityKey(backupKey);
 }