chickenchickenlove commented on code in PR #23742:
URL: https://github.com/apache/kafka/pull/23742#discussion_r4370489227
##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/modern/TargetAssignmentBuilder.java:
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@@ -158,10 +158,13 @@ private Assignment newMemberAssignment(
String memberId
) {
MemberAssignment newMemberAssignment =
newGroupAssignment.members().get(memberId);
- if (newMemberAssignment != null) {
- return new Assignment(newMemberAssignment.partitions());
- } else {
+ if (newMemberAssignment == null) {
return Assignment.EMPTY;
}
+
+ // The output is only read by the coordinator. Assignor inputs are
+ // reconstructed from target assignment records during replay.
+ // So, we don't need defensive copy here.
+ return Assignment.of(newMemberAssignment.partitions());
Review Comment:
@squah-confluent
An earlier revision made a defensive copy here. I removed it after the
discussion about whether it was necessary, reasoning that the coordinator only
reads the output and reconstructs immutable assignments during replay.
I hadn't fully considered assignor offloading. Since record building can be
delayed until after another group invokes the assignor, I agree that we should
restore the defensive copy here even if cost is quite expensive.
@dajac
What do you think?
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