hbtoo commented on a change in pull request #2187:
URL: https://github.com/apache/calcite/pull/2187#discussion_r502818769
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File path: core/src/main/java/org/apache/calcite/plan/volcano/RelSubset.java
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@@ -375,76 +373,6 @@ RelNode buildCheapestPlan(VolcanoPlanner planner) {
return cheapest;
}
- /**
- * Checks whether a relexp has made its subset cheaper, and if it so,
- * propagate new cost to parent rel nodes using breadth first manner.
- *
- * @param planner Planner
- * @param mq Metadata query
- * @param rel Relational expression whose cost has improved
- * @param activeSet Set of active subsets, for cycle detection
- */
- void propagateCostImprovements(VolcanoPlanner planner, RelMetadataQuery mq,
- RelNode rel, Set<RelSubset> activeSet) {
- Queue<Pair<RelSubset, RelNode>> propagationQueue = new ArrayDeque<>();
- for (RelSubset subset : set.subsets) {
- if (rel.getTraitSet().satisfies(subset.traitSet)) {
- propagationQueue.offer(Pair.of(subset, rel));
- }
- }
-
- while (!propagationQueue.isEmpty()) {
- Pair<RelSubset, RelNode> p = propagationQueue.poll();
- p.left.propagateCostImprovements0(planner, mq, p.right, activeSet,
propagationQueue);
- }
- }
-
- void propagateCostImprovements0(VolcanoPlanner planner, RelMetadataQuery mq,
- RelNode rel, Set<RelSubset> activeSet,
- Queue<Pair<RelSubset, RelNode>> propagationQueue) {
- ++timestamp;
-
- if (!activeSet.add(this)) {
- // This subset is already in the chain being propagated to. This
- // means that the graph is cyclic, and therefore the cost of this
- // relational expression - not this subset - must be infinite.
- LOGGER.trace("cyclic: {}", this);
Review comment:
The cyclic check is necessary for the old update logic, i.e. DFS. Now
since it is a Dijkstra like algorithm, always propagating the changed relNode
with smallest best cost, the update will automatically stop after traveling a
full cycle. So no special handling is needed any more.
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