Re: [PR] KAFKA-18901: [1/N] Improved homogeneous SimpleAssignor [kafka]

["AndrewJSchofield (via GitHub)" <gi...@apache.org>]

AndrewJSchofield commented on code in PR #19142:
URL: https://github.com/apache/kafka/pull/19142#discussion_r1984814955


##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/SimpleAssignor.java:
##########
@@ -135,56 +148,68 @@ private GroupAssignment newAssignmentHomogeneous(
         List<TopicIdPartition> targetPartitions,
         Map<TopicIdPartition, List<String>> currentAssignment
     ) {
-        Map<TopicIdPartition, List<String>> newAssignment = new HashMap<>();
-
-        // Step 1: Hash member IDs to topic partitions.
-        memberHashAssignment(targetPartitions, groupSpec.memberIds(), newAssignment);
+        int numGroupMembers = groupSpec.memberIds().size();
+        int numTargetPartitions = targetPartitions.size();
+        int desiredAssignmentCount = (numTargetPartitions + numGroupMembers - 1) / numGroupMembers;
 
-        // Step 2: Round-robin assignment for unassigned partitions which do not have members already assigned in the current assignment.
-        List<TopicIdPartition> unassignedPartitions = targetPartitions.stream()
-            .filter(targetPartition -> !newAssignment.containsKey(targetPartition))
-            .filter(targetPartition -> !currentAssignment.containsKey(targetPartition))
-            .toList();
+        Map<TopicIdPartition, List<String>> newAssignment = new HashMap<>((int) (((numTargetPartitions + 1) / 0.75f) + 1));

Review Comment:
   That's the default load factor of the Java `HashMap` which is not a public constant. What we would use in Java 19 is `HashMap.newHashMap(int)` that does approximately the same.



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