Github user jacques-n commented on the pull request:
https://github.com/apache/drill/pull/425#issuecomment-201910127
ObjectHolder should be used cautiously. That is why it is marked as
deprecated. I'm pretty sure it was deprecated when we first added it. In order
to hold complex values that can change size in aggregation, we have to hold
them in the Java heap because vectors are mutable. This is why we have
ObjectHolder, basically allows us variable width mutable values in aggregation.
It makes sense to use it here as well.
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