squah-confluent commented on code in PR #19523:
URL: https://github.com/apache/kafka/pull/19523#discussion_r2069188025
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group-coordinator/src/main/java/org/apache/kafka/coordinator/group/Group.java:
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@@ -209,4 +219,50 @@ void validateOffsetFetch(
default boolean shouldExpire() {
return true;
}
+
+ /**
+ * Computes the hash of the topics in a group.
+ *
+ * @param topicHashes The map of topic hashes. Key is topic name and value
is the topic hash.
+ * @return The hash of the group.
+ */
+ static long computeGroupHash(Map<String, Long> topicHashes) {
+ return Hashing.combineOrdered(
+ topicHashes.entrySet()
+ .stream()
+ .sorted(Map.Entry.comparingByKey())
+ .map(e -> HashCode.fromLong(e.getValue()))
+ .toList()
+ ).asLong();
+ }
+
+ /**
+ * Computes the hash of the topic id, name, number of partitions, and
partition racks by Murmur3.
+ *
+ * @param topicImage The topic image.
+ * @param clusterImage The cluster image.
+ * @return The hash of the topic.
+ */
+ static long computeTopicHash(TopicImage topicImage, ClusterImage
clusterImage) {
+ HashFunction hf = Hashing.murmur3_128();
+ Hasher topicHasher = hf.newHasher()
+ .putByte((byte) 0) // magic byte
+ .putLong(topicImage.id().hashCode()) // topic Id
+ .putString(topicImage.name(), StandardCharsets.UTF_8) // topic name
+ .putInt(topicImage.partitions().size()); // number of partitions
+
+
topicImage.partitions().entrySet().stream().sorted(Map.Entry.comparingByKey()).forEach(entry
-> {
+ topicHasher.putInt(entry.getKey()); // partition id
+ String racks = Arrays.stream(entry.getValue().replicas)
+ .mapToObj(clusterImage::broker)
+ .filter(Objects::nonNull)
+ .map(BrokerRegistration::rack)
+ .filter(Optional::isPresent)
+ .map(Optional::get)
+ .sorted()
+ .collect(Collectors.joining(";"));
Review Comment:
I think this is fine preventing for accidental collisions. Though it's still
possible to _intentionally_ come up with rack names that create collisions, but
I believe you'd only be impacting your own cluster.
To rule out any ambiguity, I'd strongly prefer if we pretended this was a
serialization format and either prefixed strings with their length, or
null-terminated them. The same for variable-length lists of strings. These can
either be length-prefixed or terminated with an invalid string that cannot
occur (""? but not sure on this).
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