Grokbase Groups HBase dev March 2013
FAQ
Rishit Shroff created HBASE-8223:
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Summary: [89-FB] Fix race condition between append/sync and HLog.close() work flow.
Key: HBASE-8223
URL: https://issues.apache.org/jira/browse/HBASE-8223
Project: HBase
Issue Type: Bug
Affects Versions: 0.89-fb
Reporter: Rishit Shroff
Priority: Minor


The RegionServer was performing a shutdown as it got YouAreDeadException. It closed the HLog and was waiting to close all the regions where it got stuck.

The reason region close is stuck because it's trying to obtain a lock which is occupied by the put op, which in turn is waiting for append to HLog to complete.

There is race condition here is between append/sync and HLog.close() work flow.

Scenario:

Thread 1 => doing the append
Thread 2 => doing HregionServer shutdown

Timeline:

t1> 1: Verifies that LogSyncer is not shutting down and HLog is not closed and calls sync()
t2> 2: HRegionServer issued HLog.close()
t3> 2: In HLog.close(), it joins the LogSyncer thread, which signals all the threads waiting on syncDone and exits.
t4> 1: In sync, it sees that the sync has not complete until its txd, hence adds itself to the syncDone.await queue.

Note: at t4, it does not check whether the LogSyncer Thread is alive or not, which caused this hang.

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postedMar 29, '13 at 7:21p
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