Add a TODO about duplicate tuples for RowBatch::DeepCopyTo
Add a TODO about duplicate tuples for RowBatch::DeepCopyTo

RowBatch::DeepCopyTo doesn't deduplicate tuples when copying. If not
used carefully, this could lead to us producing oversized row batches
(similar to the problem solved by dedup in RowBatch::Serialize).

Currently this could only occur if the build-side child of a nested loop
join both produces batches with many duplicate tuples and sets
MarkNeedToReturn.

Also fix error in comment.

Change-Id: Ib59c92f42ee4d491c9a9d55e0b125af90f2b1d48
Reviewed-on: http://gerrit.cloudera.org:8080/874
Reviewed-by: Tim Armstrong <2f8e34250f03a653da3dc27f7ec203eafdde80fc@cloudera.com>
Tested-by: Internal Jenkins

XiaominZhang/Impala,XiaominZhang/Impala,cchanning/Impala,XiaominZhang/Impala,kapilrastogi/Impala,kapilrastogi/Impala,kapilrastogi/Impala,bratatidas9/Impala-1,bowlofstew/Impala,kapilrastogi/Impala,bowlofstew/Impala,bratatidas9/Impala-1,bratatidas9/Impala-1,XiaominZhang/Impala,bowlofstew/Impala,XiaominZhang/Impala,bowlofstew/Impala,XiaominZhang/Impala,kapilrastogi/Impala,cchanning/Impala,cchanning/Impala,cchanning/Impala,bowlofstew/Impala,kapilrastogi/Impala,cchanning/Impala,kapilrastogi/Impala,cchanning/Impala,bowlofstew/Impala,bratatidas9/Impala-1,bratatidas9/Impala-1,bowlofstew/Impala,cchanning/Impala,bratatidas9/Impala-1,XiaominZhang/Impala,bratatidas9/Impala-1