himanshukandwal commented on code in PR #2778:
URL: https://github.com/apache/helix/pull/2778#discussion_r1525546851
##########
helix-core/src/main/java/org/apache/helix/controller/rebalancer/MaintenanceRebalancer.java:
##########
@@ -55,12 +59,19 @@ public IdealState computeNewIdealState(String resourceName,
IdealState currentId
// One principal is to prohibit DROP -> OFFLINE and OFFLINE -> DROP state
transitions.
// Derived preference list from current state with state priority
+ StateModelDefinition stateModelDef =
clusterData.getStateModelDef(currentIdealState.getStateModelDefRef());
+
for (Partition partition : currentStateMap.keySet()) {
Map<String, String> stateMap = currentStateMap.get(partition);
List<String> preferenceList = new ArrayList<>(stateMap.keySet());
+
+ // This sorting preserves the ordering of current state hosts in the
order of current IS pref list
Collections.sort(preferenceList, new
PreferenceListNodeComparator(stateMap,
-
clusterData.getStateModelDef(currentIdealState.getStateModelDefRef()),
- Collections.<String>emptyList()));
+ stateModelDef,
currentIdealState.getPreferenceList(partition.getPartitionName())));
+
+ // This sorts the current state hosts based on the priority
+ preferenceList.sort(new StatePriorityComparator(stateMap,
stateModelDef));
Review Comment:
So this is getting applied when we have already sorted the current state
hosts in the preference-list order. (line: 70)
```
pref-list: [A, B, C]
current-state: {
A: FOLLOWER,
B: LEADER,
C: FOLLOWER
}
```
Lets say `newPrefList = new ArrayList<>(current-state.keySet())` => `[C, B,
A]`
```
Sort 1: Sort based on preference-list order:
newPrefList = [C, B, A] => [A, B, C]
Sort 2: Sort based on state-priority order:
newPrefList = [A, B, C] => [B, A, C]
```
Here, A will be 2nd and C will be third always as both have same priority so
original (pref-list) order will be maintained.
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