public static HRegion openHRegion(Path rootDir, final RegionInfo info, final TableDescriptor htd,
    final WAL wal, final Configuration conf) throws IOException {
    return openHRegion(rootDir, info, htd, wal, conf, null, null);
  }
Open a Region.
@param rootDir Root directory for HBase instance
@param info    Info for region to be opened.
@param htd     the table descriptor
@param wal     WAL for region to use. This method will call WAL#setSequenceNumber(long) passing
               the result of the call to HRegion#getMinSequenceId() to ensure the wal id is
               properly kept up. HRegionStore does this every time it opens a new region.
@param conf    The Configuration object to use.
@return new HRegion
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java