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Date: Thu, 3 Aug 2017 22:05:00 +0000 (UTC)
From: "Jaydeepkumar Chovatia (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.13092315.1501797852000.89028.1501797900058@Atlassian.JIRA>
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Subject: [jira] [Created] (CASSANDRA-13740) Orphan hint file gets created
 while node is being removed from cluster
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archived-at: Thu, 03 Aug 2017 22:05:05 -0000

Jaydeepkumar Chovatia created CASSANDRA-13740:
-------------------------------------------------

             Summary: Orphan hint file gets created while node is being rem=
oved 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 directo=
ry forever. I debugged the code and found that it is due to the race condit=
ion between [HintsWriteExecutor.java::flush | https://github.com/apache/cas=
sandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsWriteExe=
cutor.java#L195] and [HintsWriteExecutor.java::closeWriter | https://github=
.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hint=
s/HintsWriteExecutor.java#L106]
.=20
=20
*Time t1* Node is down, as a result Hints are being written by [HintsWriteE=
xecutor.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.j=
ava-exciseStore | https://github.com/apache/cassandra/blob/cassandra-3.0/sr=
c/java/org/apache/cassandra/hints/HintsService.java#L327] which removes hin=
t files for the node being removed
*Time t3* Mutation stage keeps pumping Hints through [HintService.java::wri=
te | https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/ap=
ache/cassandra/hints/HintsService.java#L145] which again calls [HintsWriteE=
xecutor.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 h=
elped me reproduce this new bug. I will submit patch for this new dtest lat=
er.

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 lon=
ger part of the ring
2. I then tried {{nodetool truncatehints}}, that still doesn=E2=80=99t remo=
ve hint file because it is not yet included in the [dispatchDequeue | https=
://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassa=
ndra/hints/HintsStore.java#L53]


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

Solution:
This is due to race condition as mentioned above. Since {{HintsWriteExecuto=
r.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/HintsServi=
ce.java#L303] a host, just store it in-memory, and check for already evicte=
d host inside [HintsWriteExecutor.java::flush | https://github.com/apache/c=
assandra/blob/cassandra-3.0/src/java/org/apache/cassandra/hints/HintsWriteE=
xecutor.java#L215]. If already evicted host is found then ignore hints.

Jaydeep


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