Distributed log splitting deleteNode races againsth splitLog retry
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Key: HBASE-5081
URL: https://issues.apache.org/jira/browse/HBASE-5081
Project: HBase
Issue Type: Bug
Components: wal
Affects Versions: 0.92.0, 0.94.0
Reporter: Jimmy Xiang
Assignee: Jimmy Xiang
Recently, during 0.92 rc testing, we found distributed log splitting hangs
there forever. Please see attached screen shot.
I looked into it and here is what happened I think:
1. One rs died, the servershutdownhandler found it out and started the
distributed log splitting;
2. All three tasks failed, so the three tasks were deleted, asynchronously;
3. Servershutdownhandler retried the log splitting;
4. During the retrial, it created these three tasks again, and put them in a
hashmap (tasks);
5. The asynchronously deletion in step 2 finally happened for one task, in the
callback, it removed one
task in the hashmap;
6. One of the newly submitted tasks' zookeeper watcher found out that task is
unassigned, and it is not
in the hashmap, so it created a new orphan task.
7. All three tasks failed, but that task created in step 6 is an orphan so the
batch.err counter was one short,
so the log splitting hangs there and keeps waiting for the last task to finish
which is never going to happen.
So I think the problem is step 2. The fix is to make deletion sync, instead of
async, so that the retry will have
a clean start.
Async deleteNode will mess up with split log retrial. In extreme situation, if
async deleteNode doesn't happen
soon enough, some node created during the retrial could be deleted.
deleteNode should be sync.
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