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https://issues.apache.org/jira/browse/SOLR-13486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17004269#comment-17004269
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Dawid Weiss commented on SOLR-13486:
------------------------------------
I hit this very often on Linux (org.apache.solr.cloud.TestCloudConsistency) and
this prevents regular sanity-checks of the gradle branch. Is there anything
that can be done about it?
{code}
org.apache.solr.cloud.TestCloudConsistency >
testOutOfSyncReplicasCannotBecomeLeader FAILED
java.lang.AssertionError: Doc with id=4 not found in
http://127.0.0.1:40399/solr/outOfSyncReplicasCannotBecomeLeader-false due to:
Path not found: /id; rsp={doc=null}
at
__randomizedtesting.SeedInfo.seed([542A0C718771D678:2AC12C614416D942]:0)
at org.junit.Assert.fail(Assert.java:88)
at org.junit.Assert.assertTrue(Assert.java:41)
at
org.apache.solr.cloud.TestCloudConsistency.assertDocExists(TestCloudConsistency.java:285)
at
org.apache.solr.cloud.TestCloudConsistency.assertDocsExistInAllReplicas(TestCloudConsistency.java:269)
at
org.apache.solr.cloud.TestCloudConsistency.testOutOfSyncReplicasCannotBecomeLeader(TestCloudConsistency.java:140)
at
org.apache.solr.cloud.TestCloudConsistency.testOutOfSyncReplicasCannotBecomeLeader(TestCloudConsistency.java:99)
{code}
> race condition between leader's "replay on startup" and non-leader's "recover
> from leader" can leave replicas out of sync (TestCloudConsistency)
> ------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: SOLR-13486
> URL: https://issues.apache.org/jira/browse/SOLR-13486
> Project: Solr
> Issue Type: Bug
> Reporter: Chris M. Hostetter
> Priority: Major
> Attachments:
> apache_Lucene-Solr-BadApples-NightlyTests-master_61.log.txt.gz,
> apache_Lucene-Solr-BadApples-Tests-8.x_102.log.txt.gz
>
>
> I've been investigating some jenkins failures from TestCloudConsistency,
> which at first glance suggest a problem w/replica(s) recovering after a
> network partition from the leader - but in digging into the logs the root
> cause acturally seems to be a thread race conditions when a replica (the
> leader) is first registered...
> * The {{ZkContainer.registerInZk(...)}} method (which is called by
> {{CoreContainer.registerCore(...)}} & {{CoreContainer.load()}}) is typically
> run in a background thread (via the {{ZkContainer.coreZkRegister}}
> ExecutorService)
> * {{ZkContainer.registerInZk(...)}} delegates to
> {{ZKController.register(...)}} which is ultimately responsible for checking
> if there are any "old" tlogs on disk, and if so handling the "Replaying tlog
> for <URL> during startup" logic
> * Because this happens in a background thread, other logic/requests can be
> handled by this core/replica in the meantime - before it starts (or while in
> the middle of) replaying the tlogs
> ** Notably: *leader's that have not yet replayed tlogs on startup will
> erroneously respond to RTG / Fingerprint / PeerSync requests from other
> replicas w/incomplete data*
> ...In general, it seems scary / fishy to me that a replica can (aparently)
> become *ACTIVE* before it's finished it's {{registerInZk}} + "Replaying tlog
> ... during startup" logic ... particularly since this can happen even for
> replicas that are/become leaders. It seems like this could potentially cause
> a whole host of problems, only one of which manifests in this particular test
> failure:
> * *BEFORE* replicaX's "coreZkRegister" thread reaches the "Replaying tlog
> ... during startup" check:
> ** replicaX can recognize (via zk terms) that it should be the leader(X)
> ** this leaderX can then instruct some other replicaY to recover from it
> ** replicaY can send RTG / PeerSync / FetchIndex requests to the leaderX
> (either on it's own volition, or because it was instructed to by leaderX) in
> an attempt to recover
> *** the responses to these recovery requests will not include updates in the
> tlog files that existed on leaderX prior to startup that hvae not yet been
> replayed
> * *AFTER* replicaY has finished it's recovery, leaderX's "Replaying tlog ...
> during startup" can finish
> ** replicaY now thinks it is in sync with leaderX, but leaderX has
> (replayed) updates the other replicas know nothing about
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