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  1. Calcite
  2. CALCITE-4302

Improve cost propagation in volcano to avoid re-propagation

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    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 1.27.0
    • Component/s: None

      Description

      CALCITE-3330 changed the cost propagation in volcano from DFS to BFS. However, there is still room for improvement. A subset can be updated more than once in a cost propagation process. For instance, A -> D, A -> B -> C -> D. When subset A has an update, using BFS subset D (and thus all subsets above/after D) can be updated twice, first via A -> D and then C -> D. We can further improve the BFS by always popping the relNode with the smallest cost from the queue, similar to the Dijkstra algorithm. So that whenever a relNode is popped from the queue, its current best cannot be further deceased any more. As a result, all subsets will only be propagated at most once.

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              • Assignee:
                danny0405 Danny Chen
                Reporter:
                botong Botong Huang
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