Details
-
Bug
-
Status: Open
-
Major
-
Resolution: Unresolved
-
None
-
None
-
None
Description
When a connector or task tries to read the offsets from the offsets topic, it issues `OffsetStorageImpl#offsets` method. This method gets a Future from the underneath KafkaBackingStore. KafkaBackingStore invokes `KafkaBasedLog#readToEnd` method and passes the Callback. This method essentially adds the Callback to a Queue of callbacks that are being managed.
Within KafkaBasedLog, there's a WorkThread which keeps polling over the callback queue and executes them and it does this in an infinite loop. However, there is an enclosing try/catch block around the while loop. If there's an exception thrown which is not caught by any of the other catch blocks, the control goes to the outermost catch block and the WorkThread is terminated. However, the connectors/tasks are not aware of this and they would keep submitting callbacks to KafkaBasedLog with nobody processing them. This can be seen in the thread dumps as well:
"task-thread-connector-0" #6334 prio=5 os_prio=0 cpu=19.36ms elapsed=2092.93s tid=0x00007f8d9c037000 nid=0x5d00 waiting on condition [0x00007f8dc08cd000] java.lang.Thread.State: WAITING (parking) at jdk.internal.misc.Unsafe.park(java.base@11.0.15/Native Method) - parking to wait for <0x000000070345c9a8> (a java.util.concurrent.CountDownLatch$Sync) at java.util.concurrent.locks.LockSupport.park(java.base@11.0.15/LockSupport.java:194) at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(java.base@11.0.15/AbstractQueuedSynchronizer.java:885) at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(java.base@11.0.15/AbstractQueuedSynchronizer.java:1039) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(java.base@11.0.15/AbstractQueuedSynchronizer.java:1345) at java.util.concurrent.CountDownLatch.await(java.base@11.0.15/CountDownLatch.java:232) at org.apache.kafka.connect.util.ConvertingFutureCallback.get(ConvertingFutureCallback.java:98) at org.apache.kafka.connect.storage.OffsetStorageReaderImpl.offsets(OffsetStorageReaderImpl.java:101) at org.apache.kafka.connect.storage.OffsetStorageReaderImpl.offset(OffsetStorageReaderImpl.java:63)
We need a mechanism to fail all such offset read requests. That is because even if we restart the thread, chances are it will still fail with the same error so the offset fetch would be stuck perennially.