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https://issues.apache.org/jira/browse/HBASE-2645?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13491727#comment-13491727
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stack commented on HBASE-2645:
------------------------------

Adding logging, I can see the 'master' return from the recover file lease call 
against the namenode.  We then go to open the 'wal' to read the edits out of it 
splitting.  Meantime, I see that the writer thread is still progressing adding 
edits until it stalls in a sync call.  This means the read will miss edits 
(lots in this test case).
                
> HLog writer can do 1-2 sync operations after lease has been recovered for 
> split process.
> ----------------------------------------------------------------------------------------
>
>                 Key: HBASE-2645
>                 URL: https://issues.apache.org/jira/browse/HBASE-2645
>             Project: HBase
>          Issue Type: Bug
>          Components: Filters
>    Affects Versions: 0.90.4
>            Reporter: Cosmin Lehene
>            Assignee: Todd Lipcon
>            Priority: Blocker
>             Fix For: 0.96.0
>
>         Attachments: 2645.txt, 2645v2.txt, 2645v3.txt, 
> hdfs_1.0_editswriter_recoverlease.txt, 
> hdfs_trunk_editswriter_recoverlease.txt, 
> org.apache.hadoop.hbase.regionserver.wal.TestHLogSplit-output.txt
>
>
> TestHLogSplit.testLogCannotBeWrittenOnceParsed is failing. 
> This test starts a thread that writes one edit to the log, syncs and counts. 
> During this, a HLog.splitLog operation is started. splitLog recovers the log 
> lease before reading the log, so that the original regionserver could not 
> wake up and write after the split process started.  
> The test compares the number of edits reported by the split process and by 
> the writer thread. Writer thread (called zombie in the test) should report <= 
>  than the splitLog (sync() might raise after the last edit gets written and 
> the edit won't get counted by zombie thread). However it appears that the 
> zombie counts 1-2 more edits. So it looks like it can sync without a lease.
> This might be a hdfs-0.20 related issue. 

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