FrankYang0529 commented on code in PR #19523:
URL: https://github.com/apache/kafka/pull/19523#discussion_r2087031341
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group-coordinator/src/main/java/org/apache/kafka/coordinator/group/Utils.java:
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@@ -324,4 +329,84 @@ static void throwIfRegularExpressionIsInvalid(
regex, ex.getDescription()));
}
}
+
+ /**
+ * The magic byte used to identify the version of topic hash function.
+ */
+ static final byte TOPIC_HASH_MAGIC_BYTE = 0x00;
+
+ /**
+ * Computes the hash of the topics in a group.
+ * <p>
+ * The computed hash value is stored as part of the metadata hash in the
*GroupMetadataValue.
+ * <p>
+ * The hashing process involves the following steps:
+ * 1. Sort the topic hashes by topic name.
+ * 2. Write each topic hash in order.
+ *
+ * @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) {
Review Comment:
IIUC, this function will only be used in `GroupMetadataManager` like
`throwIfRegularExpressionIsInvalid`. I think we can add `public` when we need
it. WDYT?
##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/Utils.java:
##########
@@ -324,4 +329,84 @@ static void throwIfRegularExpressionIsInvalid(
regex, ex.getDescription()));
}
}
+
+ /**
+ * The magic byte used to identify the version of topic hash function.
+ */
+ static final byte TOPIC_HASH_MAGIC_BYTE = 0x00;
+
+ /**
+ * Computes the hash of the topics in a group.
+ * <p>
+ * The computed hash value is stored as part of the metadata hash in the
*GroupMetadataValue.
+ * <p>
+ * The hashing process involves the following steps:
+ * 1. Sort the topic hashes by topic name.
+ * 2. Write each topic hash in order.
+ *
+ * @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) {
+ // Sort entries by topic name
+ List<Map.Entry<String, Long>> sortedEntries = new
ArrayList<>(topicHashes.entrySet());
+ sortedEntries.sort(Map.Entry.comparingByKey());
+
+ HashStream64 hasher = Hashing.xxh3_64().hashStream();
+ for (Map.Entry<String, Long> entry : sortedEntries) {
+ hasher.putLong(entry.getValue());
+ }
+
+ return hasher.getAsLong();
+ }
+
+ /**
+ * Computes the hash of the topic id, name, number of partitions, and
partition racks by XXHash64.
+ * <p>
+ * The computed hash value for the topic is utilized in conjunction with
the {@link #computeGroupHash(Map)}
+ * method and is stored as part of the metadata hash in the
*GroupMetadataValue.
+ * It is important to note that if the hash algorithm is changed, the
magic byte must be updated to reflect the
+ * new hash version.
+ * <p>
+ * The hashing process involves the following steps:
+ * 1. Write a magic byte to denote the version of the hash function.
+ * 2. Write the hash code of the topic ID.
+ * 3. Write the topic name.
+ * 4. Write the number of partitions associated with the topic.
+ * 5. For each partition, write the partition ID and a sorted list of rack
identifiers.
+ * - Rack identifiers are formatted as
"<length1><value1><length2><value2>" to prevent issues with simple separators.
+ *
+ * @param topicImage The topic image.
+ * @param clusterImage The cluster image.
+ * @return The hash of the topic.
+ */
+ static long computeTopicHash(TopicImage topicImage, ClusterImage
clusterImage) throws IOException {
Review Comment:
Same as above.
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