TAJO-1114: Improve ConfVars (SessionVar) to take a validator interface to check its input.

[ykrips]

No description provided.

[hyunsik]

Even through it needs rebase, it was easy to merge the patch against the latest revision.

I'm reviewing this patch. I'll leave comments soon.

[hyunsik]

Shell variable (i.e., ```${user.name}) is translated in Hadoop's Configuration. Actually, this config is just a string.

[hyunsik]

Hi @ykrips,

I greatly appreciate your contribution. The patch looks really great. I love your design.

Actually, I didn't mention how we validate each config key. Of course, it is out of scope of this issue. Now, I just share it with you.

In my plan, Tajo will validate configs in two ways.

The first way is that TajoMaster validates each config when it starts up. If TajoMaster finds invalid config which probably will cause query runtime errors, TajoMaster will shutdown immediately and prints out detailed error messages. If so, we can earlier prohibit some kind of query runtime errors.

The second one is that TajoMaster checks each session setting action by client. If a client sets an invalid session variable, it will show some errors and prohibit putting the invalid variable into session variables.

If you fix the validator for tajo.username and rebase it, I'll finish the review.

Best regards,
Hyunsik

[ykrips]

Hello @hyunsik ,
I will fix some missing points for your comments, and will rebase it.
On my implementation, I have overrided some functions of Configuration class to raise exceptions when invalid values are inserted. However, with your explanation, I feel that TajoMaster will throw exceptions, not TajoConf. I just wonder if I correctly understand your strategy.

[ykrips]

Hello @hyunsik ,
I am apologized for my mistake on this pull request. I trying to rebase my local branch to github repository. But it corrupt ref files or any other files on my git repository. I'm sorry again for my mistake. And I will close and re-open this pull request.

[hyunsik]

@ykrips

No problem :)
I'll leave the comment about your question in #214.