brandboat commented on code in PR #19803:
URL: https://github.com/apache/kafka/pull/19803#discussion_r2106238196
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metadata/src/main/java/org/apache/kafka/metadata/MetadataCache.java:
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@@ -148,56 +147,53 @@ DescribeTopicPartitionsResponseData describeTopicResponse(
boolean ignoreTopicsWithExceptions);
static Cluster toCluster(String clusterId, MetadataImage image) {
- Map<Integer, List<Node>> brokerToNodes = new HashMap<>();
- image.cluster().brokers().values().stream()
- .filter(broker -> !broker.fenced())
- .forEach(broker -> brokerToNodes.put(broker.id(), broker.nodes()));
+ Map<Integer, Node> nodesById =
image.cluster().brokers().values().stream()
+ .collect(Collectors.toMap(BrokerRegistration::id, broker ->
broker.nodes().get(0)));
Review Comment:
Pardon me, I meant "replicas", not leader.
Maybe an example will help clarify things:
Let’s say we have 3 brokers — broker0, broker1, and broker2 — and a topic
called my-topic. Partition 0 of this topic has 3 replicas, one on each broker.
Now suppose broker2 unexpectedly shuts down.
Here’s what happens next:
1. DynamicTopicClusterQuotaPublisher#onMetadataUpdate gets triggered
2. That leads to MetadataCache#toCluster being called
3. In toCluster, nodesById gets constructed without the fenced broker
(broker2 is filtered out)
4. Then MetadataCache#toArray uses this nodesById, but in the TopicsImage
the PartitionRegistration (my-topic partition-0) still has replicas [0, 1, 2].
Since broker2 isn’t in nodesById, we get a NullPointerException, kaboom!
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