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https://issues.apache.org/jira/browse/SOLR-9191?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15320027#comment-15320027
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Scott Blum commented on SOLR-9191:
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Yeah, I was going to use Predicate, but wanted to be compatible with your patch
for 8744. If you're fine with Predicate, I'll use that.
> OverseerTaskQueue.peekTopN() fatally flawed
> -------------------------------------------
>
> Key: SOLR-9191
> URL: https://issues.apache.org/jira/browse/SOLR-9191
> Project: Solr
> Issue Type: Bug
> Affects Versions: 5.4, 5.4.1, 5.5, 5.5.1, 6.0, 6.0.1
> Reporter: Scott Blum
> Assignee: Scott Blum
> Priority: Blocker
> Fix For: 5.6, 6.1, 5.5.2, 6.0.2, 6.2
>
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> We rewrote DistributedQueue in SOLR-6760, to optimize its obvious use case as
> a FIFO. But in doing so, we broke the assumptions in
> OverseerTaskQueue.peekTopN()..
> OverseerTaskQueue.peekTopN() involves filtering out items you're already
> working on, it's trying to peek for new items in the queue beyond what you
> already know about. But DistributedQueue (being designed as a FIFO) doesn't
> know about the filtering; as long as it has any items in-memory it just keeps
> returning those over and over without ever pulling new data from ZK. This is
> true even if the watcher has fired and marked the state as dirty. So
> OverseerTaskQueue gets into a state where it can never read new items in ZK
> because DQ keeps returning the same items that it has marked as in-progress.
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