@Override
    public int commit() {
        int allNew = 0;
        writeLock.lock();
        try {
            for (int i = 0; i < 256; ++i) {
                allNew += files[i].getNewKeys();
                files[i].commit();
            }
        } finally {
            writeLock.unlock();
        }
        return  allNew;
    }