hbtoo commented on a change in pull request #2187:
URL: https://github.com/apache/calcite/pull/2187#discussion_r503026189
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File path:
core/src/main/java/org/apache/calcite/plan/volcano/VolcanoPlanner.java
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@@ -906,6 +903,67 @@ void rename(RelNode rel) {
}
}
+ /**
+ * Checks whether a relexp has made any subset cheaper, and if it so,
+ * propagate new cost to parent rel nodes.
+ *
+ * @param rel Relational expression whose cost has improved
+ */
+ void propagateCostImprovements(RelNode rel) {
+ RelMetadataQuery mq = rel.getCluster().getMetadataQuery();
+ Map<RelNode, RelOptCost> propagateRels = new HashMap<>();
+ PriorityQueue<RelNode> propagateHeap = new PriorityQueue<>((o1, o2) -> {
+ RelOptCost c1 = propagateRels.get(o1);
Review comment:
If you consider cost as a kind of distance between relnodes/subsets,
this propagation process is basically Dijkstra in a directed graph. Computing
the best plan in this directed graph is finding the "shortest" path.
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