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https://issues.apache.org/jira/browse/SOLR-14505?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17113005#comment-17113005
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Colvin Cowie commented on SOLR-14505:
-------------------------------------
Oh dear, another race condition: I created
https://issues.apache.org/jira/browse/SOLR-14504 a little while ago :)
> Intermittent NPE in ZkController.registerLiveNodesListener()
> ------------------------------------------------------------
>
> Key: SOLR-14505
> URL: https://issues.apache.org/jira/browse/SOLR-14505
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Affects Versions: 8.3.1
> Reporter: Andrzej Bialecki
> Assignee: Andrzej Bialecki
> Priority: Minor
>
> Reported by [~cjcowie] in SOLR-13072 & mailing lists:
> "Running on Solr 8.3.1
> {code:java}
> 2020-05-19 03:44:40.220 INFO (main) [ ] o.a.s.c.ZkContainer Zookeeper
> client=XXXXXXXXX:9983/xxxx_cluster
> 2020-05-19 03:44:40.238 INFO (main) [ ] o.a.s.c.c.SolrZkClient Using
> ZkCredentialsProvider:
> xxxxxxx.zookeeper.auth.internal.EncodedZkCredentialsProvider
> 2020-05-19 03:44:40.241 INFO (main) [ ] o.a.s.c.c.ConnectionManager
> Waiting for client to connect to ZooKeeper
> 2020-05-19 03:44:40.245 INFO (zkConnectionManagerCallback-11-thread-1) [ ]
> o.a.s.c.c.ConnectionManager zkClient has connected
> 2020-05-19 03:44:40.245 INFO (main) [ ] o.a.s.c.c.ConnectionManager Client
> is connected to ZooKeeper
> 2020-05-19 03:44:40.359 INFO (main) [ ] o.a.s.c.c.ConnectionManager
> Waiting for client to connect to ZooKeeper
> 2020-05-19 03:44:40.361 INFO (zkConnectionManagerCallback-13-thread-1) [ ]
> o.a.s.c.c.ConnectionManager zkClient has connected
> 2020-05-19 03:44:40.361 INFO (main) [ ] o.a.s.c.c.ConnectionManager Client
> is connected to ZooKeeper
> 2020-05-19 03:44:40.417 INFO (main) [ ] o.a.s.c.c.ZkStateReader Updated
> live nodes from ZooKeeper... (0) -> (1)
> 2020-05-19 03:44:56.606 INFO (zkCallback-12-thread-2) [ ]
> o.a.s.c.c.ZkStateReader Updated live nodes from ZooKeeper... (1) -> (0)
> 2020-05-19 03:44:56.614 ERROR (main) [ ] o.a.s.s.SolrDispatchFilter Could
> not start Solr. Check solr/home property and the logs
> 2020-05-19 03:44:56.639 ERROR (main) [ ] o.a.s.c.SolrCore
> null:java.lang.NullPointerException
> at
> org.apache.solr.cloud.ZkController.lambda$registerLiveNodesListener$10(ZkController.java:1020)
> at
> org.apache.solr.common.cloud.ZkStateReader.registerLiveNodesListener(ZkStateReader.java:880)
> at
> org.apache.solr.cloud.ZkController.registerLiveNodesListener(ZkController.java:1035)
> at org.apache.solr.cloud.ZkController.init(ZkController.java:917)
> at org.apache.solr.cloud.ZkController.<init>(ZkController.java:473)
> at org.apache.solr.core.ZkContainer.initZooKeeper(ZkContainer.java:115)
> at org.apache.solr.core.CoreContainer.load(CoreContainer.java:631)at
> xxxxxxx.solr.servlet.RobustSolrDispatchFilter.createCoreContainer(RobustSolrDispatchFilter.java:71)
> {code}
> I couldn't find any bug reports in JIRA for the NPE.
>
> Here's the full log
> [https://drive.google.com/open?id=1hQrF25blNgKLXijOMYJ30wn-Lfy6uKVm]
>
> The NPE is coming from
> [https://github.com/apache/lucene-solr/blob/c18666ad05afc02979c150aacd4810cff02e43f3/solr/core/src/java/org/apache/solr/cloud/ZkController.java#L1020]
>
> _byte[] json = Utils.toJSON(Collections.singletonMap("timestamp",
> cloudManager.getTimeSource().getEpochTimeNs()));_
> so I don't know whether it's the cloudManager or the time source that's null.
> That bit of the ZkController was added by
> https://issues.apache.org/jira/browse/SOLR-13072 and I see it is only hit if
>
> _zkStateReader.getAutoScalingConfig().hasTriggerForEvents(TriggerEventType.NODELOST);_
>
> We have never (knowingly) configured autoscaling and we don't use it, but I
> see the autoscaling files are present in ZK. Is the autoscaling.json etc
> created by default when it is absent in ZooKeeper?
>
> The interesting bit of the log above, aside from the NPE, is this:
> _2020-05-19 03:44:40.417 INFO (main) [ ] o.a.s.c.c.ZkStateReader Updated
> live nodes from ZooKeeper... (0) -> (1)_
> _2020-05-19 03:44:56.606 INFO (zkCallback-12-thread-2) [ ]
> o.a.s.c.c.ZkStateReader Updated live nodes from ZooKeeper... (1) -> (0)_
> Which suggests to me that there's either a race condition or the problem is
> caused by some zookeeper outage during startup. Since there's a 16 second gap
> between those messages.
>
> It's possible that the problem is in some way caused by our own code in
> xxxxxxx.solr.servlet.RobustSolrDispatchFilter which wraps the
> SolrDispatchFIlter, and creates a SolrZkClient in a try/with resources (so
> should be autoclosed), but that all happens before createCoreContainer is
> called."
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