kirktrue commented on code in PR #18795:
URL: https://github.com/apache/kafka/pull/18795#discussion_r1940329129
##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractFetch.java:
##########
@@ -408,22 +407,52 @@ protected Map<Node, FetchSessionHandler.FetchRequestData>
prepareFetchRequests()
long currentTimeMs = time.milliseconds();
Map<String, Uuid> topicIds = metadata.topicIds();
- for (TopicPartition partition : fetchablePartitions()) {
- SubscriptionState.FetchPosition position =
subscriptions.position(partition);
+ // This is the set of partitions that have buffered data
+ Set<TopicPartition> buffered =
Collections.unmodifiableSet(fetchBuffer.bufferedPartitions());
- if (position == null)
- throw new IllegalStateException("Missing position for
fetchable partition " + partition);
+ // This is the set of partitions that do not have buffered data
+ Set<TopicPartition> unbuffered = fetchablePartitions(buffered);
- Optional<Node> leaderOpt = position.currentLeader.leader;
+ if (unbuffered.isEmpty()) {
+ // If there are no partitions that don't already have data locally
buffered, there's no need to issue
+ // any fetch requests at the present time.
+ return Collections.emptyMap();
+ }
- if (leaderOpt.isEmpty()) {
- log.debug("Requesting metadata update for partition {} since
the position {} is missing the current leader node", partition, position);
- metadata.requestUpdate(false);
+ Set<Integer> bufferedNodes = new HashSet<>();
+
+ for (TopicPartition partition : buffered) {
+ // It's possible that at the time of the fetcher creating new
fetch requests, a partition with buffered
+ // data from a *previous* request is no longer assigned. So before
attempting to retrieve the node
+ // information, check that the partition is still assigned and
fetchable; an unassigned/invalid partition
+ // will throw an IllegalStateException in positionForPartition.
+ //
+ // Note: this check is not needed for the unbuffered partitions as
the logic in
+ // SubscriptionState.fetchablePartitions() only includes
partitions currently assigned.
+ if (!subscriptions.hasValidPosition(partition))
+ continue;
+
+ // A paused partition remains in the fetch buffer even though it's
not returned to the user. Unless
+ // this case is handled, a paused partition will inadvertently
"block" a request from being created to
+ // fetch data for other partitions, leading users to poll
indefinitely waiting for more data.
+ //
+ // See FetchCollector.collectFetch().
+ if (subscriptions.isPaused(partition))
+ continue;
Review Comment:
FYI: I updated the comment after adding my reviewers’ notes.
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
