kirktrue commented on code in PR #16310:
URL: https://github.com/apache/kafka/pull/16310#discussion_r1640101706
##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/AsyncKafkaConsumer.java:
##########
@@ -1666,23 +1668,68 @@ private boolean initWithCommittedOffsetsIfNeeded(Timer
timer) {
return true;
log.debug("Refreshing committed offsets for partitions {}",
initializingPartitions);
+
+ // The shorter the timeout provided to poll(), the more likely the
offsets fetch will time out. To handle
+ // this case, on the first attempt to fetch the committed offsets, a
FetchCommittedOffsetsEvent is created
+ // (with potentially a longer timeout) and stored. The event is used
for the first attempt, but in the
+ // case it times out, subsequent attempts will also use the event in
order to wait for the results.
+ if (!canReusePendingOffsetFetchEvent(initializingPartitions)) {
+ // Give the event a reasonable amount of time to complete.
+ final long timeoutMs = Math.max(defaultApiTimeoutMs,
timer.remainingMs());
+ final long deadlineMs = calculateDeadlineMs(time, timeoutMs);
+ pendingOffsetFetchEvent = new
FetchCommittedOffsetsEvent(initializingPartitions, deadlineMs);
+ applicationEventHandler.add(pendingOffsetFetchEvent);
+ }
+
+ final CompletableFuture<Map<TopicPartition, OffsetAndMetadata>> future
= pendingOffsetFetchEvent.future();
+ boolean shouldClearPendingEvent = false;
+
try {
- final FetchCommittedOffsetsEvent event =
- new FetchCommittedOffsetsEvent(
- initializingPartitions,
- calculateDeadlineMs(timer));
- wakeupTrigger.setActiveTask(event.future());
- final Map<TopicPartition, OffsetAndMetadata> offsets =
applicationEventHandler.addAndGet(event);
+ wakeupTrigger.setActiveTask(future);
+ final Map<TopicPartition, OffsetAndMetadata> offsets =
ConsumerUtils.getResult(future, timer);
+
+ // Clear the pending event once its result is successfully
retrieved.
+ shouldClearPendingEvent = true;
+
refreshCommittedOffsets(offsets, metadata, subscriptions);
return true;
} catch (TimeoutException e) {
log.error("Couldn't refresh committed offsets before timeout
expired");
return false;
+ } catch (InterruptException e) {
+ throw e;
+ } catch (Throwable t) {
+ // Clear the pending event on errors that are not timeout- or
interrupt-related.
+ shouldClearPendingEvent = true;
+ throw ConsumerUtils.maybeWrapAsKafkaException(t);
} finally {
+ if (shouldClearPendingEvent)
+ pendingOffsetFetchEvent = null;
+
wakeupTrigger.clearTask();
}
}
+ /**
+ * This determines if the {@link #pendingOffsetFetchEvent pending offset
fetch event} can be reused. Reuse
+ * is only possible if all the following conditions are true:
+ *
+ * <ul>
+ * <li>A pending offset fetch event exists</li>
+ * <li>The partition set of the pending offset fetch event is the same
as the given partition set</li>
+ * <li>The pending offset fetch event has not expired</li>
+ * </ul>
+ */
+ private boolean canReusePendingOffsetFetchEvent(Set<TopicPartition>
partitions) {
+ if (pendingOffsetFetchEvent == null)
+ return false;
+
+ if (!pendingOffsetFetchEvent.partitions().equals(partitions))
Review Comment:
@chia7712—that's definitely an interesting optimization!
IIUC, the suggestion is to relax the requirement to allow reuse if the
partitions for the _current_ request are a subset of (or equal to) the
_previous_ request, right? So basically:
```suggestion
if (!pendingOffsetFetchEvent.partitions().containsAll(partitions))
```
The behavior of the existing `LegacyKafkaConsumer` is to allow reuse only if
the partitions for the _current_ request equal those of the _previous_ request
**exactly**
([source](https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinator.java#L927)).
That logic is the basis for the behavior used in the `AsyncKafkaConsumer`.
We've been very deliberate to try to match the behavior between the two
`Consumer` implementations as closely as possible, unless there's a specific
reason not to.
It's a small change, and it does makes sense (to me). My main concern is
that it introduces a subtle difference in behavior between the two `Consumer`
implementations. Also, the specific case we're trying to solve with this change
is when the user has passed in a very low timeout and we're in a tight `poll()`
loop, which suggests the partitions wouldn't be changing between those loops
(CMIIW).
If I understand correctly, this seems like an optimization, rather than
something needed for correctness. If that's the case, can I file a new Jira to
implement this when we have a little more time to investigate and test?
Thanks!
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