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https://issues.apache.org/jira/browse/HBASE-14495?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14908979#comment-14908979
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stack commented on HBASE-14495:
-------------------------------
This looks legit. Am having trouble trying to figure how MVCC gets into a state
such that it has an incomplete write ahead of the flush mvcc...
> TestHRegion#testFlushCacheWhileScanning goes zombie
> ---------------------------------------------------
>
> Key: HBASE-14495
> URL: https://issues.apache.org/jira/browse/HBASE-14495
> Project: HBase
> Issue Type: Sub-task
> Components: test
> Reporter: stack
> Assignee: stack
>
> This test goes zombie on us, most recently, here:
> https://builds.apache.org/job/PreCommit-HBASE-Build/15744//console
> It does not fail on my internal rig runs nor locally on laptop when run in a
> loop.
> Its hung up in close of the region:
> {code}
> "main" prio=10 tid=0x00007fc49800a800 nid=0x6053 in Object.wait()
> [0x00007fc4a02c9000]
> java.lang.Thread.State: WAITING (on object monitor)
> at java.lang.Object.wait(Native Method)
> - waiting on <0x00000007d07c3478> (a java.lang.Object)
> at
> org.apache.hadoop.hbase.regionserver.MultiVersionConcurrencyControl.waitForRead(MultiVersionConcurrencyControl.java:207)
> - locked <0x00000007d07c3478> (a java.lang.Object)
> at
> org.apache.hadoop.hbase.regionserver.MultiVersionConcurrencyControl.completeAndWait(MultiVersionConcurrencyControl.java:143)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.internalPrepareFlushCache(HRegion.java:2257)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:2061)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:2026)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:2016)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.doClose(HRegion.java:1423)
> at org.apache.hadoop.hbase.regionserver.HRegion.close(HRegion.java:1344)
> - locked <0x00000007d07c34a8> (a java.lang.Object)
> at org.apache.hadoop.hbase.regionserver.HRegion.close(HRegion.java:1295)
> at
> org.apache.hadoop.hbase.HBaseTestingUtility.closeRegionAndWAL(HBaseTestingUtility.java:352)
> at
> org.apache.hadoop.hbase.regionserver.TestHRegion.testFlushCacheWhileScanning(TestHRegion.java:3756)
> {code}
> It is waiting on mvcc to catch up.
> There is this comment at the point where we are hung:
> // TODO: Lets see if we hang here, if there is a scenario where
> an outstanding reader
> // with a read point is in advance of this write point.
> mvcc.completeAndWait(writeEntry);
> The above came in with HBASE-12751. The comment was added at v29:
> https://issues.apache.org/jira/secure/attachment/12754775/12751.rebased.v29.txt
> Looks like I added it so must have had predilection that this might be
> dodgy... Let me take a look...
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