Dan Hecht has posted comments on this change.

Change subject: IMPALA-3586: Implement union passthrough
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Patch Set 11:

> No, we do not break out of the loop, we return right away (see line
 > 149 in the original union-node.cc). The next getnext call can
 > return 0 rows.

I'm talking about the case where we don't hit the limit. We normally won't take 
the return at line 149 (unless we happen to fill the row batch at the same time 
as finishing the children, but that's not the usual case). Instead, if we still 
have room after evaluating the children (and constant exprs), we'll get all the 
way to 192.  So, the normal non-limit case is inconsistently handled.  I agree 
it's not a functional bug, though.

It'd still be nice to exercise the multiple child row-batch path, if we're not 
already. Hopefully we already are (row-batch-size might be a exec option 
dimension in pytest), but I just thought it'd be good to check that.

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Gerrit-MessageType: comment
Gerrit-Change-Id: Ia8f6d5062724ba5b78174c3227a7a796d10d8416
Gerrit-PatchSet: 11
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Taras Bobrovytsky <[email protected]>
Gerrit-Reviewer: Alex Behm <[email protected]>
Gerrit-Reviewer: Dan Hecht <[email protected]>
Gerrit-Reviewer: Marcel Kornacker <[email protected]>
Gerrit-Reviewer: Taras Bobrovytsky <[email protected]>
Gerrit-Reviewer: Tim Armstrong <[email protected]>
Gerrit-HasComments: No

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