private long postAppend(final Entry e, final long elapsedTime) throws IOException {
    long len = 0;
    if (!listeners.isEmpty()) {
      for (Cell cell : e.getEdit().getCells()) {
        len += PrivateCellUtil.estimatedSerializedSizeOf(cell);
      }
      for (WALActionsListener listener : listeners) {
        listener.postAppend(len, elapsedTime, e.getKey(), e.getEdit());
      }
    }
    return len;
  }
Exposed for testing only. Use to tricks like halt the ring buffer appending.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AbstractFSWAL.java