lucasbru commented on code in PR #22552:
URL: https://github.com/apache/kafka/pull/22552#discussion_r3418882759
##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/StreamsGroupHeartbeatResult.java:
##########
@@ -26,20 +26,40 @@
/**
* A simple record to hold the result of a StreamsGroupHeartbeat request.
*
- * @param data The data to be returned to the client.
- * @param creatableTopics The internal topics to be created.
- * @param currentTopologyEpoch The topology epoch the group is operating at
after this heartbeat, or -1 if the
- * group has no topology yet. The service layer
uses this to decide whether to set
- * TopologyDescriptionRequired on the response
(KIP-1331).
+ * <p>The three epoch fields let the service layer decide, without re-reading
the group,
+ * whether to set {@code TopologyDescriptionRequired} on the response: a push
is needed
+ * when the stored epoch lags the current epoch and the same epoch has not
already been
+ * recorded as a permanent failure. All three are -1 for failure-fast paths
that do not
+ * resolve a group.
+ *
+ * @param data The data to be returned to the
client.
+ * @param creatableTopics The internal topics to be created.
+ * @param currentTopologyEpoch The topology epoch the group is
operating at after this heartbeat,
+ * or -1 if the group has no topology
yet.
+ * @param storedDescriptionTopologyEpoch The most recent topology epoch
successfully stored by the topology
+ * description plugin, or -1 if none.
+ * @param failedDescriptionTopologyEpoch The most recent topology epoch the
plugin permanently rejected,
+ * or -1 if none.
*/
public record StreamsGroupHeartbeatResult(
StreamsGroupHeartbeatResponseData data,
Map<String, CreatableTopic> creatableTopics,
- int currentTopologyEpoch
+ int currentTopologyEpoch,
Review Comment:
These three trailing epochs are all ints, and the 1-arg convenience ctor
fills them with -1. A future construction site that transposes two of them, or
uses the convenience ctor on a real-group path, compiles clean and silently
disables (or wrongly triggers) solicitation. Might be worth an epoch-bundle
type, or deriving the epochs from the group in GMM, rather than three
positional ints at each site.
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