BackendArchitectX commented on code in PR #19915:
URL: https://github.com/apache/pinot/pull/19915#discussion_r4345289536
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pinot-broker/src/main/java/org/apache/pinot/broker/routing/instanceselector/ReplicaGroupInstanceSelector.java:
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@@ -73,6 +75,45 @@ public class ReplicaGroupInstanceSelector extends
BaseInstanceSelector {
private static final Logger LOGGER =
LoggerFactory.getLogger(ReplicaGroupInstanceSelector.class);
+ // Immutable key for instance groups that reduces hash collisions.
+ static final class InstanceSetKey implements Comparable<InstanceSetKey> {
+ private final String[] _instances;
+ private final int _hashCode;
+
+ InstanceSetKey(Set<String> instances) {
+ _instances = instances.toArray(new String[0]);
+ Arrays.sort(_instances);
+
+ int hash = 1;
+ for (String instance : _instances) {
+ hash = 31 * hash + HashCommon.mix(instance.hashCode());
+ }
+ _hashCode = hash;
+ }
+
+ @Override
+ public int hashCode() {
+ return _hashCode;
+ }
+
+ @Override
+ public boolean equals(Object object) {
+ if (this == object) {
+ return true;
+ }
+ if (!(object instanceof InstanceSetKey)) {
+ return false;
+ }
+ InstanceSetKey other = (InstanceSetKey) object;
+ return _hashCode == other._hashCode && Arrays.equals(_instances,
other._instances);
+ }
+
+ @Override
+ public int compareTo(InstanceSetKey other) {
Review Comment:
Thanks for the review! I kept `Comparable` intentionally because `HashMap`
uses it to navigate treeified collision buckets when keys have identical
hashes. Since this change specifically addresses hash-collision performance, I
think it's worth retaining as a safeguard against residual collisions.
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