Zsolt Venczel commented on HDFS-6681:

I had verified that the test was indeed flaky without the patch (failed 3 times 
from 1000) but after applying the patch it got stable (no failures from 1000 
+1 from me.


> TestRBWBlockInvalidation#testBlockInvalidationWhenRBWReplicaMissedInDN is 
> flaky and sometimes gets stuck in infinite loops
> --------------------------------------------------------------------------------------------------------------------------
>                 Key: HDFS-6681
>                 URL: https://issues.apache.org/jira/browse/HDFS-6681
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.4.1
>         Environment: Java(TM) SE Runtime Environment (build 1.6.0_31-b04)
> Java HotSpot(TM) 64-Bit Server VM (build 20.6-b01, mixed mode)
> Linux [hostname] 2.6.32-279.14.1.el6.x86_64 #1 SMP Mon Oct 15 13:44:51 EDT 
> 2012 x86_64 x86_64 x86_64 GNU/Linux
>            Reporter: Ratandeep Ratti
>            Assignee: Ratandeep Ratti
>            Priority: Major
>              Labels: BB2015-05-TBR, flaky-test
>         Attachments: HDFS-6681.001.patch, HDFS-6681.patch
> This testcase has 3 infinite loops which break only on certain conditions 
> being satisfied.
> 1st loop checks if there should be a single live replica. It assumes this to 
> be true since it has just corrupted a block on one of the datanodes (testcase 
> has replication factor as 2). One scenario in which this loop will never 
> break is if the Namenode invalidates the corrupt replica, schedules a 
> replication command, and the new copied replica is added all before this 
> testcase has the chance to check the live-replica count.
> 2nd loop checks there should be 2 live replicas. It assumes this to be true 
> (in some time) since the first loop has broken implying there is a single 
> replica and now it is only a matter of time when the Namenode schedules a 
> replication command to copy a replica to another datanode. One scenario in 
> which this loop will never break is when the Namenode tries to schedule a new 
> replica on the same node on which we actually corrupted the block. That dst. 
> datanode will not copy the block, complaining that it already has the 
> (corrupted) replica in the create state. The situation that results is that 
> Namenode has scheduled a copy to a datanode, the block is now in the 
> namenode's pending replication queue, this block will never be removed from 
> the pending replication queue because the namenode will never receive a 
> report from the datanodes that the block is 'added'.
> Note: The block can be transferred from the 'pending replication' to "needed 
> replication" queue once the pending timeout (5 minutes) expires. The Namenode 
> then actively tries to schedule a replication for blocks in 'needed 
> replication' queue. This can cause the 2nd loop to break but the time in 
> which this process gets kicked in is more than 5 minutes.
> 3rd loop: This loops checks if there are no corrupt replicas. I don't see a 
> scenario in which this loop can go on for ever, since once the live replica 
> count goes back to normal (2), the corrupted block will be removed
> I guess increasing the heart beat interval time, so that the testcase has 
> enough time to check condition in loop 1 before a datanode reports a 
> successful copy should help avoid race condition in loop1. Regarding loop2 I 
> guess we can reduce the timeout after which the block is transferred from the 
> pending replication to the needed replication queue.

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