Hi Jinho Kim, thanks for your great contribution!
But, I think that we need to schedule every queries submitted to Tajo including locally-executed queries and DDLs.
The main application of this feature is the table-level concurrency control to handle concurrent operation for the same table.
For example, drop table operations for a table should not be executed while any pre-submitted DML queries for the same table are executed.
So, if you can do easily, do you mind including this feature to the patch?
Otherwise, I'll do at a different issue.