[jira] [Created] (HDFS-16689) Standby NameNode crashes when transitioning to Active with in-progress tailer

["ZanderXu (Jira)" <ji...@apache.org>]

ZanderXu created HDFS-16689:
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             Summary: Standby NameNode crashes when transitioning to Active with in-progress tailer
                 Key: HDFS-16689
                 URL: https://issues.apache.org/jira/browse/HDFS-16689
             Project: Hadoop HDFS
          Issue Type: Bug
            Reporter: ZanderXu
            Assignee: ZanderXu


Standby NameNode crashes when transitioning to Active with a in-progress tailer. And the error message like blew:


{code:java}
Caused by: java.lang.IllegalStateException: Cannot start writing at txid X when there is a stream available for read: ByteStringEditLog[X, Y], ByteStringEditLog[X, 0]
	at org.apache.hadoop.hdfs.server.namenode.FSEditLog.openForWrite(FSEditLog.java:344)
	at org.apache.hadoop.hdfs.server.namenode.FSEditLogAsync.openForWrite(FSEditLogAsync.java:113)
	at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startActiveServices(FSNamesystem.java:1423)
	at org.apache.hadoop.hdfs.server.namenode.NameNode$NameNodeHAContext.startActiveServices(NameNode.java:2132)
	... 36 more
{code}

After tracing and found there is a critical bug in *EditlogTailer#catchupDuringFailover()* when *DFS_HA_TAILEDITS_INPROGRESS_KEY* is true. Because *catchupDuringFailover()* try to replay all missed edits from JournalNodes with *onlyDurableTxns=true*. It may cannot replay any edits when they are some abnormal JournalNodes. 

Reproduce method, suppose:
- There are 2 namenode, namely NN0 and NN1, and the status of echo namenode is Active, Standby respectively. And there are 3 JournalNodes, namely JN0, JN1 and JN2. 
- NN0 try to sync 3 edits to JNs with started txid 3, but only successfully synced them to JN1 and JN3. And JN0 is abnormal, such as GC, bad network or restarted.
- NN1's lastAppliedTxId is 2, and at the moment, we are trying failover active from NN0 to NN1. 
- NN1 only got two responses from JN0 and JN1 when it try to selecting inputStreams with *fromTxnId=3*  and *onlyDurableTxns=true*, and the count txid of response is 0, 3 respectively. JN2 is abnormal, such as GC,  bad network or restarted.
- NN1 will cannot replay any Edits with *fromTxnId=3* from JournalNodes because the *maxAllowedTxns* is 0.


So I think Standby NameNode should *catchupDuringFailover()* with *onlyDurableTxns=true* , so that it can replay all missed edits from JournalNode.



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