void updateBlockBytesScanned(long blockBytesScanned) {
      prevBlockBytesScannedDifference = blockBytesScanned - prevBlockBytesScanned;
      prevBlockBytesScanned = blockBytesScanned;
      if (blockBytesScanned > maxBlockBytesScanned) {
        maxBlockBytesScanned = blockBytesScanned;
      }
    }
Holder class which holds the RegionScanner, nextCallSeq and RpcCallbacks together.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSRpcServices.java