Github user hyunsik commented on the pull request:

    https://github.com/apache/tajo/pull/192#issuecomment-60460566
  
    This work looks great. Please keep going! Actually, this work already has 
or will face many challenges. It is definitely worthy to challenge the problems.
    
    I leave some comments. Actually, I just look over the design and the 
overall approach because this patch will be committed to ```index_support``` 
branch. When the patch is merged to ```master``` branch, I'll review it in 
implementation level.
    
    In addition, you seem to already have experiment environments. If possible, 
could you share the performances with varying selectivity? It's not requirement 
for this patch. But, we need to estimate the performance gain when we adopt 
indexing approach. Although your benchmark result looks nice, 
````0.000045139%``` is too low selectivity in practice.
    
    As we discussed, index size is very important. If we don't have efficient 
index structure, this feature won't be used in practice. As we discussed, we 
need to investigate more efficient ones.


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