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https://issues.apache.org/jira/browse/HDFS-6599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14371310#comment-14371310
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Kihwal Lee commented on HDFS-6599:
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There have been many performance improvements since 2.3. Examples: HDFS-7097 
and HDFS-7615 fix writers being unfairly penalized.  HDFS-7217 reduces the 
write locking of namesystem by 30-40%. This is a big deal for busy clusters. If 
you use the audit logging, try async audit logging (HDFS-5241). This should be 
already in 2.3.

> 2.4 addBlock is 10 to 20 times slower compared to 0.23
> ------------------------------------------------------
>
>                 Key: HDFS-6599
>                 URL: https://issues.apache.org/jira/browse/HDFS-6599
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.3.0, 2.4.0
>            Reporter: Kihwal Lee
>            Assignee: Daryn Sharp
>            Priority: Blocker
>             Fix For: 2.5.0
>
>         Attachments: HDFS-6599.patch
>
>
> From one of our busiest 0.23 clusters:
> {panel}
> "AddBlockAvgTime" : 0.9514711501719515
> "CreateAvgTime" : 1.7564162389174
> "CompleteAvgTime" : 1.3310406035056548
> "BlockReceivedAndDeletedAvgTime" : 0.661210005151392
> {panel}
> From a not-so-busy 2.4 cluster:
> {panel}
> "AddBlockAvgTime" : 10.083333333333334
> "CreateAvgTime" : 1.0
> "CompleteAvgTime" : 1.1111111111111112
> "BlockReceivedAndDeletedAvgTime" : 0.07692307692307694
> {panel}
> When the 2.4 cluster gets a moderate amount of write requests, the latency is 
> terrible. E.g. addBlock goes upward of 60ms. 



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