xndai opened a new pull request #1440: [CALCITE-2166] Cumulative cost of RelSubset.best RelNode is increased… URL: https://github.com/apache/calcite/pull/1440 … after calling RelSubset.propagateCostImprovements() for input RelNodes It's possible that Subset's best cost increases when input subset's best is changed. In those cases, although input subset's cost is reduced, the row count can increase which causes the increase of non-cumulative cost of parent rel. As a result, the cost of parent rel can increase. If the parent rel happens to be the best rel of a given subset, we currently do nothing. And this would lead to the inconsistency of the rel node cost. Fixing this by updating the best rel node cost if it's increased. Although this approach won't garantee an optimal plan, at least it makes sure the memo is consistent. More details, please refer to JIRA - https://issues.apache.org/jira/browse/CALCITE-2166
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