poorbarcode commented on code in PR #24366:
URL: https://github.com/apache/pulsar/pull/24366#discussion_r2118803149
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pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java:
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@@ -1510,6 +1511,28 @@ private CompletableFuture<Void> delete(boolean
failIfHasSubscriptions,
}
fenceTopicToCloseOrDelete(); // Avoid clients reconnections while
deleting
+ // Wait compaction to avoid a deadlock below:
+ // 1. thread-compaction : create a raw reader.
+ // 2. thread-topic-deleting : mark topic as deleting, and
disconnect clients that includes compaction
+ // reader.
+ // 3. thread-compaction: the raw reader attempts to reconnect due
to the disconnection in step "2-1".
+ // 4. thread-topic-deleting: unsubscribe all subscriptions, which
contains "__compaction".
+ // 5. thread-topic-deleting: deleting "__compaction" cursor will
wait for the in-progress compaction task.
+ // 6. thread-compaction: the raw read can not connect successfully
anymore because the topic was marked as
+ // "fenced && isDeleting".
+ // 7. deadlock: "thread-topic-deleting" waiting for compaction
task being finished, thread-compaction
+ // continuously reconnects.
+ // To solve the issue, let "thread-topic-deleting" release the
fencing&deleting state, wait for the
+ // compaction task being finished. Since "thread-topic-deleting"
never release "lock.writeLock", the broker
+ // will not trigger a new compaction task.
+ if (currentCompaction != null && !currentCompaction.isDone()) {
+ unfenceTopicToResume();
Review Comment:
The current task will set `isFenced` and `isClosingOrDeleting` to `true`
here(https://github.com/apache/pulsar/pull/24366/files#diff-5edf14cc6f25857d0cfdd26b2d3b3141230ecfb0dfa95aebf7583fd76ede4c4bR1513),
the method `unfenceTopicToResume` is the negative method of
`fenceTopicToCloseOrDelete`.
There is no protection of guaranteeing `isFenced` and `isClosingOrDeleting`
atomically modifying, but it was not introduced in the current PR. We may need
to merge `transferring`, `isFenced`, and `isClosingOrDeleting` into one in a
separate PR to guarantee atomicity
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