swuferhong opened a new pull request, #1666:
URL: https://github.com/apache/fluss/pull/1666
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### Purpose
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Linked issue: close #1665
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This pr is aims to Fix the TimeoutException of MetadataRequest sent by
LogFetcher when upgrading cluster. The root cause of this issue is that both
`LogFetcher#sendFetches()` and `LogFetcher#handleFetchLogResponse()` hold the
synchronized lock simultaneously. Specifically:
1. `sendFetches()` initiates a metadata operation that sends a
`MetadataRequest` while holding the lock.
2. `handleFetchLogResponse()` is triggered in the `whenComplete()` method of
`FetchLogRequest`. The caller of `whenComplete()` –
`ServerConnection.ResponseCallback#onRequestResult(int requestId, ApiMessage
response)` – blocks the Netty client worker thread.
Deadlock Scenario:
- When `LogFetcher` triggers a `MetadataRequest`, it holds the synchronized
lock of `LogFetcher`.
- Simultaneously, multiple `FetchLogResponses` return to `Netty client
workers` (whose count is controlled by
`client.netty.client.num-network-threads`).
- These responses invoke `ResponseCallback#onRequestResult`, which occupies
the `Netty worker threads` and waits for the same `LogFetcher` lock.
- Result: Deadlock occurs because:
a) The `MetadataResponse` cannot acquire a `Netty worker thread`
(blocked by `FetchLogResponse` processing)
b) `FetchLogResponse` processing waits indefinitely for the `LogFetcher`
lock (held by `MetadataRequest`).
- Eventually, the `MetadataRequest` times out. After timeout,
`ResponseCallback#onRequestResult` finally acquires the lock and recovers.
### Brief change log
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they address the issue -->
### Tests
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### API and Format
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### Documentation
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