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https://issues.apache.org/jira/browse/HDFS-4882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14222737#comment-14222737
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Yongjun Zhang commented on HDFS-4882:
-------------------------------------
Hi [~cmccabe] and [~vinayrpet],
Thanks for your comments.
{quote}
can you comment on whether you have also observed this bug?
{quote}
Yes, I did observe a similar infinite loop, and by studying the code, I
concluded that the case I was looking at has exactly the same root cause as the
one reported here. Please see details described in my earlier comment at
https://issues.apache.org/jira/browse/HDFS-4882?focusedCommentId=14213992&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14213992,
the several comments after that.
In short, when the penultimate block is COMMITTED and the last block is
COMPLETE, the following block of code will be executed
{code}
switch(lastBlockState) {
case COMPLETE:
assert false : "Already checked that the last block is incomplete";
break;
{code}
and return back to LeaseManager without releasing the corresponding lease,
which stays as the first element in {{sortedLeases}}. The leaseManager keeps
examining the first entry in sortedLease again and again, while holding the
FSNamesystem#writeLock, thus causing the infinite loop.
{quote}
Yes, you are right. Even though I don't see the possibility of infinite loop by
considering existing code in trunk, changes made in the patch looks pretty cool.
{quote}
See above for the explanation about infinite loop in the existing code.
{quote}
Yes, lets continue this discussion in HDFS-7342
{quote}
In HDFS-7342, Ravi worked out a testcase to demonstrate the problem and I
suggested a solution. Thanks in advance for your review and comments there.
Hope we can get to a converged solution soon. Since avoiding infinite loop is
just part of the complete solution, and the other part is to get the lease
released, which is what HDFS-7342 tries to address.
Thanks.
> Namenode LeaseManager checkLeases() runs into infinite loop
> -----------------------------------------------------------
>
> Key: HDFS-4882
> URL: https://issues.apache.org/jira/browse/HDFS-4882
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client, namenode
> Affects Versions: 2.0.0-alpha, 2.5.1
> Reporter: Zesheng Wu
> Assignee: Ravi Prakash
> Priority: Critical
> Attachments: 4882.1.patch, 4882.patch, 4882.patch, HDFS-4882.1.patch,
> HDFS-4882.2.patch, HDFS-4882.3.patch, HDFS-4882.4.patch, HDFS-4882.5.patch,
> HDFS-4882.6.patch, HDFS-4882.7.patch, HDFS-4882.patch
>
>
> Scenario:
> 1. cluster with 4 DNs
> 2. the size of the file to be written is a little more than one block
> 3. write the first block to 3 DNs, DN1->DN2->DN3
> 4. all the data packets of first block is successfully acked and the client
> sets the pipeline stage to PIPELINE_CLOSE, but the last packet isn't sent out
> 5. DN2 and DN3 are down
> 6. client recovers the pipeline, but no new DN is added to the pipeline
> because of the current pipeline stage is PIPELINE_CLOSE
> 7. client continuously writes the last block, and try to close the file after
> written all the data
> 8. NN finds that the penultimate block doesn't has enough replica(our
> dfs.namenode.replication.min=2), and the client's close runs into indefinite
> loop(HDFS-2936), and at the same time, NN makes the last block's state to
> COMPLETE
> 9. shutdown the client
> 10. the file's lease exceeds hard limit
> 11. LeaseManager realizes that and begin to do lease recovery by call
> fsnamesystem.internalReleaseLease()
> 12. but the last block's state is COMPLETE, and this triggers lease manager's
> infinite loop and prints massive logs like this:
> {noformat}
> 2013-06-05,17:42:25,695 INFO
> org.apache.hadoop.hdfs.server.namenode.LeaseManager: Lease [Lease. Holder:
> DFSClient_NONMAPREDUCE_-1252656407_1, pendingcreates: 1] has expired hard
> limit
> 2013-06-05,17:42:25,695 INFO
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Recovering lease=[Lease.
> Holder: DFSClient_NONMAPREDUCE_-1252656407_1, pendingcreates: 1], src=
> /user/h_wuzesheng/test.dat
> 2013-06-05,17:42:25,695 WARN org.apache.hadoop.hdfs.StateChange: DIR*
> NameSystem.internalReleaseLease: File = /user/h_wuzesheng/test.dat, block
> blk_-7028017402720175688_1202597,
> lastBLockState=COMPLETE
> 2013-06-05,17:42:25,695 INFO
> org.apache.hadoop.hdfs.server.namenode.LeaseManager: Started block recovery
> for file /user/h_wuzesheng/test.dat lease [Lease. Holder: DFSClient_NONM
> APREDUCE_-1252656407_1, pendingcreates: 1]
> {noformat}
> (the 3rd line log is a debug log added by us)
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