@Override
  protected void deserializeStateData(ProcedureStateSerializer serializer) throws IOException {
    super.deserializeStateData(serializer);

    MasterProcedureProtos.ModifyNamespaceStateData modifyNamespaceMsg =
      serializer.deserialize(MasterProcedureProtos.ModifyNamespaceStateData.class);
    newNsDescriptor =
      ProtobufUtil.toNamespaceDescriptor(modifyNamespaceMsg.getNamespaceDescriptor());
    if (modifyNamespaceMsg.hasUnmodifiedNamespaceDescriptor()) {
      oldNsDescriptor =
        ProtobufUtil.toNamespaceDescriptor(modifyNamespaceMsg.getUnmodifiedNamespaceDescriptor());
    }
  }
The procedure to add a namespace to an existing table.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/procedure/ModifyNamespaceProcedure.java