adixitconfluent commented on PR #17965:
URL: https://github.com/apache/kafka/pull/17965#issuecomment-2509650770
> @adixitconfluent Thanks for the PR, but for my understanding when can this
scenario happen? We take a lock in the `acquire` which means a single
thread/client can have access. And acquire method is synchronous update hence
state will be fully transitioned. How do we encounter this issue?
@apoorvmittal10, the issue can occur when the writeState RPC hasn't
completed writing updates to the persister for AVAILABLE records which could
result in leaked/null `acquisitionLockTimeoutTask`. Quoting the issue mentioned
on the ticket for details-
`SharePartition#acquire` does not honor the rollback state [1][2]. This
causes two issues.
a. leaked `acquisitionLockTimeoutTask - `SharePartition#acquire` create a
new `acquisitionLockTimeoutTask` for the "available" batch, however, the
available batch in transition already has a `acquisitionLockTimeoutTask`, so
the leaked `acquisitionLockTimeoutTask` will corrupt the state later ...
b. null `acquisitionLockTimeoutTask` in a "acquired" batch - this can be
reproduced by following order.
the batch is in transition - current state is `AVAILABLE` and rollback state
is `ACQUIRED`
`SharePartition#rollbackOrProcessStateUpdates` is processing RPC, so it does
not call `InFlightState#completeStateTransition`
`SharePartition#acquire` assumes the batch is available, so it changes the
state from `AVAILABLE` to `ACQUIRED` and create a new
`acquisitionLockTimeoutTask` (see a.)
`SharePartition#rollbackOrProcessStateUpdates` complete the RPC - it commit
the state and cancel the `acquisitionLockTimeoutTask` - that means the batch is
in `ACQUIRED` but it does not have `acquisitionLockTimeoutTask`
the next AcknowledgeRequest tries to update the state to `ACKNOWLEDGED` but
it encounters NPE `acquisitionLockTimeoutTask`[3] and then the request gets
hanging until timeout
[1]
https://github.com/apache/kafka/blob/trunk/core/src/main/java/kafka/server/share/SharePartition.java#L665
[2]
https://github.com/apache/kafka/blob/trunk/core/src/main/java/kafka/server/share/SharePartition.java#L646
[3]
https://github.com/apache/kafka/blob/trunk/core/src/main/java/kafka/server/share/SharePartition.java#L1663
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