protected KeyValueScanner createScanner(Scan scan, ScanInfo scanInfo,
    NavigableSet<byte[]> targetCols, long readPt) throws IOException {
    return scan.isReversed()
      ? new ReversedStoreScanner(this, scanInfo, scan, targetCols, readPt)
      : new StoreScanner(this, scanInfo, scan, targetCols, readPt);
  }
Return a scanner for both the memstore and the HStore files. Assumes we are not in a
compaction.
@param scan       Scan to apply when scanning the stores
@param targetCols columns to scan
@return a scanner over the current key values
@throws IOException on failure
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java