morrySnow commented on code in PR #15833:
URL: https://github.com/apache/doris/pull/15833#discussion_r1067844668
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fe/fe-core/src/main/java/org/apache/doris/nereids/memo/Memo.java:
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@@ -465,6 +468,8 @@ public Group mergeGroup(Group source, Group destination) {
source.moveOwnership(destination);
groups.remove(source.getGroupId());
}
+
+ needMergeGroups.forEach(this::mergeGroup);
Review Comment:
consider a scenario:
if we have two entry in the map: B -> A and C -> B.
when we do merge group. we first merge B to A, and then B is removed. after
that, we want to merge C to B, but B is not exist anymore.
So, maybe we need to use **disjoint set** do find a common parent, and then
merge all other group to it in one **disjoint set**.
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