public static AssignRegionHandler create(HRegionServer server, RegionInfo regionInfo,
    long openProcId, TableDescriptor tableDesc, long masterSystemTime,
    long initiatingMasterActiveTime) {
    EventType eventType;
    if (regionInfo.isMetaRegion()) {
      eventType = EventType.M_RS_OPEN_META;
    } else if (
      regionInfo.getTable().isSystemTable()
        || (tableDesc != null && tableDesc.getPriority() >= HConstants.ADMIN_QOS)
    ) {
      eventType = EventType.M_RS_OPEN_PRIORITY_REGION;
    } else {
      eventType = EventType.M_RS_OPEN_REGION;
    }
    return new AssignRegionHandler(server, regionInfo, openProcId, tableDesc, masterSystemTime,
      initiatingMasterActiveTime, eventType);
  }
Handles opening of a region on a region server.
<p/>
Just done the same thing with the old {@link OpenRegionHandler}, with some modifications on
fencing and retrying. But we need to keep the {@link OpenRegionHandler} as is to keep compatible
with the zk less assignment for 1.x, otherwise it is not possible to do rolling upgrade.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/handler/AssignRegionHandler.java