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https://issues.apache.org/jira/browse/HDFS-12278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16120217#comment-16120217
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Daryn Sharp commented on HDFS-12278:
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For context regarding the impact of the change to a priority queue: Hours
after a 2.8 upgrade, avg rpc processing time increased from sub-ms to 21ms.
Rpc queue time was multiple seconds. Killing large jobs only made it worse.
The fair call queue was completely overflowing for ~5h. I haven't seen
anything this horrific in many years.
While the NN log was spewing logs of skipping calls from timing out clients, we
noticed lease monitor recovery log messages ~5-12ms apart during which time the
lease monitor holds the write lock. Killing jobs made it worse because it
created more orphaned leases.
> LeaseManager#removeLease operation is inefficient in 2.8.
> ---------------------------------------------------------
>
> Key: HDFS-12278
> URL: https://issues.apache.org/jira/browse/HDFS-12278
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.8.0
> Reporter: Rushabh S Shah
> Assignee: Rushabh S Shah
> Priority: Blocker
>
> After HDFS-6757, LeaseManager #removeLease became expensive.
> HDFS-6757 changed the {{sortedLeases}} object from TreeSet to PriorityQueue.
> Previously the {{remove(Object)}} operation from {{sortedLeases}} was {{O(log
> n)}} but after the change it became {{O( n)}} since it has to find the object
> first.
> Recently we had an incident in one of our production cluster just hours after
> we upgraded from 2.7 to 2.8
> The {{sortledLeases}} object had approximately 100,000 items within it.
> While removing the lease, it will acquire the LeaseManager lock and that will
> slow down the lookup of lease also.
> HDFS-6757 is a good improvement which replaced the path by inode id.
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