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https://issues.apache.org/jira/browse/SOLR-8697?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15159610#comment-15159610
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Scott Blum commented on SOLR-8697:
----------------------------------
Actually, I'm stupid. The flaky problem is that I *still* didn't fix the race
regarding leaderZkNodeParentVersion. I just made it harder to repro.
The smoking gun is this line:
{code}
log.info("No version found for ephemeral leader parent node, won't remove
previous leader registration.");
{code}
You can repro this pretty easily with the following change:
{code}
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
-- a/solr/core/src/java/org/apache/solr/cloud/ElectionContext.java
++ b/solr/core/src/java/org/apache/solr/cloud/ElectionContext.java
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
@@ -193,7 +193,7 @@ class ShardLeaderElectionContextBase extends
ElectionContext {
List<OpResult> results;
results = zkClient.multi(ops, true);
Thread.sleep(10000);
for (OpResult result : results) {
if (result.getType() == ZooDefs.OpCode.setData) {
SetDataResult dresult = (SetDataResult) result;
{code}
We need a harder synchronization around becoming leader vs. canceling.
> Fix LeaderElector issues
> ------------------------
>
> Key: SOLR-8697
> URL: https://issues.apache.org/jira/browse/SOLR-8697
> Project: Solr
> Issue Type: Bug
> Components: SolrCloud
> Affects Versions: 5.4.1
> Reporter: Scott Blum
> Assignee: Mark Miller
> Labels: patch, reliability, solrcloud
> Fix For: master
>
> Attachments: OverseerTestFail.log, SOLR-8697-followup.patch,
> SOLR-8697.patch
>
>
> This patch is still somewhat WIP for a couple of reasons:
> 1) Still debugging test failures.
> 2) This will more scrutiny from knowledgable folks!
> There are some subtle bugs with the current implementation of LeaderElector,
> best demonstrated by the following test:
> 1) Start up a small single-node solrcloud. it should be become Overseer.
> 2) kill -9 the solrcloud process and immediately start a new one.
> 3) The new process won't become overseer. The old process's ZK leader elect
> node has not yet disappeared, and the new process fails to set appropriate
> watches.
> NOTE: this is only reproducible if the new node is able to start up and join
> the election quickly.
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