Jaydeepkumar Chovatia created CASSANDRA-13740:
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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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