docs: @Override
      public int size(PersistentStore store) {
  
          int count = 0;
  
          readLock.lock();
  
          try {
              RowIterator it = firstRow(null, store);
  
              while (it.hasNext()) {
                  it.getNextRow();
  
                  count++;
              }
  
              return count;
          } finally {
              readLock.unlock();
          }
      }