code: protected void onAfterDeleteFromMemcached( @Nonnull final String sessionId ) {
          final long start = System.currentTimeMillis();
  
          final String validityInfoKey = _sessionIdFormat.createValidityInfoKeyName( sessionId );
          _storage.delete( validityInfoKey );
  
          if (_storeSecondaryBackup) {
              try {
                  _storage.delete(_sessionIdFormat.createBackupKey(sessionId));
                  _storage.delete(_sessionIdFormat.createBackupKey(validityInfoKey));
              } catch (Exception e) {
                  _log.info("Could not delete backup data for session " + sessionId + " (not critical, data will be evicted by memcached automatically).", e);
              }
          }
  
          _stats.registerSince( NON_STICKY_AFTER_DELETE_FROM_MEMCACHED, start );
      }
docs: Invoked after a non-sticky session is removed from memcached.