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https://issues.apache.org/jira/browse/HDFS-12278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16120702#comment-16120702
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Rushabh S Shah commented on HDFS-12278:
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bq. but how did you benchmark TreeSet and PriorityQueue
[~daryn] benchmarked.
He just created lease-like objects and tested renew like methods.
Basically an object with string, int member variable and a comparator.
He created 100,000 such objects and called renew on them and measured via
{{monotonicTime}}.
Daryn: please correct me if I am wrong.
bq. Are you aware of JMH?
I wasn't aware until I read the comment as did web search.
But it is very simple to understand that priority queue is not a good data
structure if you want to remove any object other than the top one.
> LeaseManager operations are 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
> Attachments: HDFS-12278-branch-2.8.001.patch, HDFS-12278.patch
>
>
> 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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