private void ponderNextBufferToRead(Position readPos) {
    if (readPos.offset >= wbSize) {
      ++readPos.bufferIndex;
      readPos.buffer = writeBuffers.get(readPos.bufferIndex);
      readPos.offset = 0;
    }
  }
THIS METHOD IS NOT THREAD-SAFE. Use only at load time (or be mindful of thread safety).
serde/src/java/org/apache/hadoop/hive/serde2/WriteBuffers.java