jiajunwang commented on a change in pull request #639: Refine the WAGED
rebalancer to minimize the partial rebalance workload.
URL: https://github.com/apache/helix/pull/639#discussion_r352895899
##########
File path:
helix-core/src/main/java/org/apache/helix/controller/rebalancer/waged/model/ClusterModelProvider.java
##########
@@ -93,42 +187,126 @@ public static ClusterModel
generateClusterModel(ResourceControllerDataProvider d
return new ClusterModel(context, toBeAssignedReplicas, assignableNodes);
}
+ // Filter the replicas map so only the replicas that have been allocated in
the existing
+ // assignmentMap remain in the map.
+ private static void removeUnknownReplicas(Map<String,
Set<AssignableReplica>> replicaMap,
+ Map<String, ResourceAssignment> assignmentMap) {
+ replicaMap.entrySet().parallelStream().forEach(replicaSetEntry -> {
+ // <partition, <state, instances set>>
+ Map<String, Map<String, Set<String>>> stateInstanceMap =
+ getStateInstanceMap(assignmentMap.get(replicaSetEntry.getKey()));
+ // Iterate the replicas of the resource to find the ones that require
reallocating.
+ Iterator<AssignableReplica> replicaIter =
replicaSetEntry.getValue().iterator();
+ while (replicaIter.hasNext()) {
+ AssignableReplica replica = replicaIter.next();
+ Set<String> validInstances =
+ stateInstanceMap.getOrDefault(replica.getPartitionName(),
Collections.emptyMap())
+ .getOrDefault(replica.getReplicaState(),
Collections.emptySet());
+ if (validInstances.isEmpty()) {
+ // Removing by comparing with the baseline assignment.
+ replicaIter.remove();
+ } else {
+ // Cleanup the state map record, so the selected instance won't be
picked up again for
+ // the other replica checkup.
+ validInstances.remove(validInstances.iterator().next());
+ }
+ }
+ });
+ }
+
/**
- * Generate a cluster model based on the current state output and data cache.
- * @param dataProvider The controller's data cache.
- * @param resourceMap The full list of the resources to be
rebalanced. Note that any
- * resources that are not in this list will be
removed from the
- * final assignment.
- * @param currentStateAssignment The resource assignment built from current
state output.
- * @return A cluster model based on the current state and data cache.
+ * Find the minimum set of replicas that need to be reassigned by comparing
with the Baseline
+ * assignment.
+ * A replica needs to be reassigned if one of the following conditions is
true:
+ * 1. The assignments in the Baseline and the Best possible assignment are
different. And the
+ * assignment in the Baseline is valid. So it is worthwhile to move it.
+ * 2. The assignments is not in the Baseline or the Best possible assignment.
+ * Otherwise, the rebalancer just keeps the current Best possible assignment
allocation.
+ *
+ * @param replicaMap A map contains all the replicas grouped by
resource name.
+ * @param activeInstances All the instances that are live and enabled
according to the delay rebalance configuration.
+ * @param baselineAssignment The baseline assignment.
+ * @param bestPossibleAssignment The current best possible assignment.
+ * @param allocatedReplicas Return the allocated replicas grouped by
the target instance name.
+ * @return The replicas that need to be reassigned.
*/
- public static ClusterModel generateClusterModelFromCurrentState(
- ResourceControllerDataProvider dataProvider,
- Map<String, Resource> resourceMap,
- Map<String, ResourceAssignment> currentStateAssignment) {
- return generateClusterModel(dataProvider, resourceMap,
dataProvider.getEnabledLiveInstances(),
- Collections.emptyMap(), Collections.emptyMap(),
currentStateAssignment);
+ private static Set<AssignableReplica>
findToBeAssignedReplicasByComparingBaseline(
+ Map<String, Set<AssignableReplica>> replicaMap, Set<String>
activeInstances,
+ Map<String, ResourceAssignment> baselineAssignment,
+ Map<String, ResourceAssignment> bestPossibleAssignment,
+ Map<String, Set<AssignableReplica>> allocatedReplicas) {
+ Set<AssignableReplica> toBeAssignedReplicas = new HashSet<>();
+ // check each resource to identify the allocated replicas and
to-be-assigned replicas.
+ for (String resourceName : replicaMap.keySet()) {
+ // <partition, <state, instances set>>
+ Map<String, Map<String, Set<String>>> baselinePartitionStateMap =
+ getValidStateInstanceMap(baselineAssignment.get(resourceName),
activeInstances);
+ Map<String, Map<String, Set<String>>> bestPossiblePartitionStateMap =
+ getValidStateInstanceMap(bestPossibleAssignment.get(resourceName),
activeInstances);
+ // Iterate the replicas of the resource to find the ones that require
reallocating.
+ for (AssignableReplica replica : replicaMap.get(resourceName)) {
+ String partitionName = replica.getPartitionName();
+ String replicaState = replica.getReplicaState();
+ // Find the allocation in the baseline
+ Set<String> baselineAllocations =
+ baselinePartitionStateMap.getOrDefault(partitionName,
Collections.emptyMap())
+ .getOrDefault(replicaState, Collections.emptySet());
+ Set<String> bestPossibleAllocations =
+ bestPossiblePartitionStateMap.getOrDefault(partitionName,
Collections.emptyMap())
+ .getOrDefault(replicaState, Collections.emptySet());
+
+ // Compare between the baseline and best possible assignments.
+ List<String> commonAllocations = new
ArrayList<>(bestPossibleAllocations);
+ commonAllocations.retainAll(baselineAllocations);
+ if (!commonAllocations.isEmpty()) {
+ // 1. If the partition is allocated at the same location in both
baseline and best possible
+ // assignment, there is no need to reassign it.
+ String allocatedInstance = commonAllocations.get(0);
+ allocatedReplicas.computeIfAbsent(allocatedInstance, key -> new
HashSet<>()).add(replica);
+ // clean up the record to prevent the same location being processed
again.
+ baselineAllocations.remove(allocatedInstance);
+ bestPossibleAllocations.remove(allocatedInstance);
+ } else if (!baselineAllocations.isEmpty()) {
+ // 2. If the partition is allocated at an active instance in the
Baseline but the
+ // allocation does not exist in the best possible assignment, try to
rebalance it.
+ toBeAssignedReplicas.add(replica);
+ // clean up the baseline record to prevent the same location being
picked up again.
Review comment:
Completely necessary. Please check the code carefully.
We are firstly looping on the replica set. The internal instance iteration
is reset every time. The current loop is not efficient, but it is the cleanest
way.
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