[GitHub] [calcite] danny0405 commented on issue #1354: [CALCITE-482] Implement sql and planner hints

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danny0405 commented on issue #1354: [CALCITE-482] Implement sql and planner hints
URL: https://github.com/apache/calcite/pull/1354#issuecomment-518536813
 
 
   > Glad to see your effort driving this long-expected feature! Here're my questions for the overall implementation(Please correct me if I understand incorrectly):
   > 
   > 1. The `HintStrategy` & `HintStrategies` abstraction: I understand this try to make the hint strategy some how pluggable but limited to pre-defined types (`QUERY`, `JOIN`, `TABLE_SCAN` and `PROJECT`) that different engines can not customize it since they may have various requirements. I think we should figure out a more flexible way to target this.
   > 2. I like the idea of the two kinds of hints: top-level (query) hint & table hint that most RDBMS vendors support, I'm not sure if necessary to add  the `hint` types for current `SqlHint`?
   > 3. The `inheritPath` in `RelHint` looks designed to represent the hints inheritance, but in current implementation the hints propagation is incomplete that only `Join`, `TableScan` and `Project` node will store the corresponding hints info, so the `inheritPath` is broken,  is it as your expects?
   
   1. `HintStrategy` is not designed to be pluggable, i think no one knows how to make it to be, if you want to support a new node, there needs some modifications(the node and the logic to propagate), then just add a new enum val.
   2. The `HintStrategy` is already kind of `hint` types, is can be used to distinguish what kind of node this hint expects to apply to, what the usage of what you proposed ?
   3. Yes, it is expected, AFAIK, the only usage of `inheritPath` is to resolve conflict when there are multiple same name `hints` for a node. And what do you mean by `broken`, the inherit path is complete (from the root node).
   

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