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https://issues.apache.org/jira/browse/CALCITE-3896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17080614#comment-17080614
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Haisheng Yuan commented on CALCITE-3896:
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1. As described in the issue, the redundancy *can't* be avoided given the
current design that physical operator must decide its children's required
traits when it is created. Solving it requires overhaul of planner, and the
implementation rules, which is a big task. This JIRA is not intended to solve
this problem.
2. All the logical and physical rules must be finished before enforcing. All
the alternatives generated by implementation rule are valid.
3. Given a specific required traitSet, passThough generates 1 or none. Can you
give an example to generate multiple candidates?
> Pass through parent trait requests to child operators
> -----------------------------------------------------
>
> Key: CALCITE-3896
> URL: https://issues.apache.org/jira/browse/CALCITE-3896
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Haisheng Yuan
> Priority: Major
>
> This is not on-demand trait requests as described in [mailing
> list|http://mail-archives.apache.org/mod_mbox/calcite-dev/201910.mbox/%3cd75b20f4-542a-4a73-897e-66ab426494c1.h.y...@alibaba-inc.com%3e],
> which requires the overhaul of the core planner. This ticket tries to enable
> VolcanoPlanner with basic and minimal ability to pass through parent trait
> request to child operators without rules, though may not be flexible or
> powerful, but should be able to work with current Calcite application with
> minimal changes.
> The method for physical operators to implement would be:
> {code:java}
> interface RelNode {
> RelNode passThrough(RelTraitSet required);
> }
> {code}
> Given that Calcite's physical operators decides its child operators' traits
> when the physical operator is created in physical implementation rule, there
> are some drawback that can't be avoided. e.g., given the following plan:
> {code:java}
> StreamAgg on [a]
> +-- MergeJoin on [a, b, c]
> |--- TableScan foo
> +--- TableScan bar
> {code}
> Suppose the MergeJoin implementation rule generates several mergejoins that
> distributes by [a], [a,b], [a,b,c] separately. Then we pass parent operator
> StreamAgg's trait request to MergeJoin. Since MergeJoin[a] satisfies parent's
> request, nothing to do. Next pass request to MergeJoin[a,b], we get
> MergeJoin[a], then pass request to MergeJoin[a,b,c], we get MergeJoin[a]
> again. We know they are redundant and there is no need to pass through parent
> operator's trait request, but these MergeJoin operators are independent and
> agnostic of each other's existence.
> The ideal way is that in physical implementation rule, during the creation of
> physical operator, it should not care about itself and its child operators'
> physical traits. But this is another different topic.
> Anyway, better than nothing, once it is done, we can provide the option to
> obsolete or disable {{AbstractConverter}}, but still be able to do property
> enforcement.
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