@Override
  public void decommissionRegionServers(List<ServerName> servers, boolean offload)
    throws IOException {
    get(admin.decommissionRegionServers(servers, offload));
  }
The {@link Admin} implementation which is based on an {@link AsyncAdmin}.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AdminOverAsyncAdmin.java