Some times RelSet can get merged. e.g.
Each number represet Rel id, and they are in different RelSet.
Assume in the rulequeue, we have rule match with name of 12, 23, 43. For simplicity, omit the rule name, first digit represent the parent RelNode, second represent the child.
If after some rule, we merged the set of 3 into the set of 2, and RelNode 4's input is replaced by RelSubset of 2. We will retrigger rules and try to add rulematch 12, 42, 43 into rule queue.
12 will be filtered out, because there is duplicate in the RuleMatch names set. But for 43, it now has different rulematch digest with previous match, because RelNode #4's input RelSubset changed, its digest also changed. So we can't detect the duplication and will re-apply rulematch 43 twice.
Although we try to recompute rulematch's digest when popMatch(), but it seems too late.
I think in RuleMatch digest, just using relnode's id should suffice. And we don't need to call recomputeDigest when popMatch.