Github user hyunsik commented on the pull request:
https://github.com/apache/tajo/pull/593#issuecomment-121105576
I'm leaving additional comments.
* Nested if-condition branches in JoinedRelationsVertex::buildPlan for
left-deep tree can be simplified. If you intend better code readability, it
would be Ok.
* isSymmetricJoinOnly in JoinGraph only seems to be affected by only the
last addJoin() call. But, its name and isSymmetricJoinOnly() name seems that
this join graph consists of only symmetric joins.
* JoinGraph::addJoin cuts the cyclic if it find out the loop. It would be
Ok in the current implementation. As a database researcher and aside from this
patch, I have just a question. Arbitrary cyclic cuts like this can lose the
better join opportunities. Is this singular position true? I'm just wondering.
If so, should we find a join order from just a join graph even including loops?
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