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From "Jaydeepkumar Chovatia (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-13740) Orphan hint file gets created while node is being removed from cluster
Date Thu, 03 Aug 2017 22:05:00 GMT
Jaydeepkumar Chovatia created CASSANDRA-13740:
-------------------------------------------------

             Summary: Orphan hint file gets created while node is being removed from cluster
                 Key: CASSANDRA-13740
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13740
             Project: Cassandra
          Issue Type: Bug
          Components: Core
            Reporter: Jaydeepkumar Chovatia
             Fix For: 3.0.15
         Attachments: gossip_hang_test.py

I have found this new issue during my test, whenever node is being removed then hint file
for that node gets written and stays inside the hint directory forever. I debugged the code
and found that it is due to the race condition between [HintsWriteExecutor.java::flush | https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsWriteExecutor.java#L195]
and [HintsWriteExecutor.java::closeWriter | https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsWriteExecutor.java#L106]
. 
 
*Time t1* Node is down, as a result Hints are being written by [HintsWriteExecutor.java::flush
| https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsWriteExecutor.java#L195]
*Time t2* Node is removed from cluster as a result it calls [HintsService.java-exciseStore
| https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsService.java#L327]
which removes hint files for the node being removed
*Time t3* Mutation stage keeps pumping Hints through [HintService.java::write | https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsService.java#L145]
which again calls [HintsWriteExecutor.java::flush | https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsWriteExecutor.java#L215]
and new orphan file gets created

I was writing a new dtest for {CASSANDRA-13562, CASSANDRA-13308} and that helped me reproduce
this new bug. I will submit patch for this new dtest later.

I also tried following to check how this orphan hint file responds:
1. I tried {{nodetool truncatehints <node>}} but it fails as node is no longer part
of the ring
2. I then tried {{nodetool truncatehints}}, that still doesn’t remove hint file because
it is not yet included in the [dispatchDequeue | https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsStore.java#L53]


Reproducible steps:
Please find dTest python file {{gossip_hang_test.py}} attached which reproduces this bug.

Solution:
This is due to race condition as mentioned above. Since {{HintsWriteExecutor.java}} creates
thread pool with only 1 worker, so solution becomes little simple. Whenever we [HintService.java::excise
| https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsService.java#L303]
a host, just store it in-memory, and check for already evicted host inside [HintsWriteExecutor.java::flush
| https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsWriteExecutor.java#L215].
If already evicted host is found then ignore hints.

Jaydeep



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