Github user jihoonson commented on a diff in the pull request:

    https://github.com/apache/tajo/pull/613#discussion_r33417668
  
    --- Diff: 
tajo-core/src/main/java/org/apache/tajo/engine/planner/physical/SeqScanExec.java
 ---
    @@ -167,23 +162,55 @@ public void init() throws IOException {
           projected = outSchema;
         }
     
    -    initScanner(projected);
    -    super.init();
    -
    -    if (plan.hasQual()) {
    -      if (scanner.isProjectable()) {
    -        qual.bind(context.getEvalContext(), projected);
    -      } else {
    -        qual.bind(context.getEvalContext(), inSchema);
    -      }
    +    return projected;
    +  }
     
    +  private void initScanIterator() {
    +    // We should use FilterScanIterator only if underlying storage does 
not support filter push down.
    --- End diff --
    
    We currently have two kinds of scan operator, sequential scan 
(```SeqScanExec``` and ```PartitionMergeScanExec```) and index scan 
(```BSTIndexScanExec```). 
    In the case of when an index exists for a HDFS table, index scan will do 
the same operation of ```FullScanIterator```. So, there seems an unified 
interface for index scan and ```FullScanIterator```.
    
    Maybe, we design a new scanner for HDFS like ```IndexedScanner```. If so, 
we can also handle index scan in the below code block.
    What do you think? Do you have any plans for this?


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