Custom Mapper and Reducer vs HiveQL
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**Problem Statement:-**

I need to compare two tables `Table1` and `Table2` and they both store same thing. So I need to compare `Table2` with `Table1` as `Table1` is the main table through which comparisons need to be made. So after comparing I need to make a report that `Table2` has some sort of discrepancy. And these two tables has lots of data, around  TB of data. So currently I have written `HiveQL` to do the comparisons and get the data back. 

So my question is which is better in terms of `PERFORMANCE`, writing a `CUSTOM MAPPER and REDUCER` to do this kind of job or the `HiveQL` that I wrote will be fine as I will be joining these two tables on millions of records. As far as I know `HiveQL` internally (behind the scenes) generates optimized custom map-reducer and submits for execution and gets back the results.