@Override
    public Pair<Path, Path> call() throws IOException {
      return splitStoreFile(regionFs, htd, hcd, sf);
    }
Constructor that takes what it needs to split
@param regionFs the file system
@param hcd      Family that contains the store file
@param sf       which file
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/SplitTableRegionProcedure.java