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https://issues.apache.org/jira/browse/HDFS-15610?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lokesh Jain resolved HDFS-15610.
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Fix Version/s: 3.4.0
Resolution: Fixed
> Reduce datanode upgrade/hardlink thread
> ---------------------------------------
>
> Key: HDFS-15610
> URL: https://issues.apache.org/jira/browse/HDFS-15610
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 3.0.0, 3.1.4
> Reporter: Karthik Palanisamy
> Assignee: Karthik Palanisamy
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.4.0
>
> Time Spent: 50m
> Remaining Estimate: 0h
>
> There is a kernel overhead on datanode upgrade. If datanode with millions of
> blocks and 10+ disks then block-layout migration will be super expensive
> during its hardlink operation. Slowness is observed when running with large
> hardlink threads(dfs.datanode.block.id.layout.upgrade.threads, default is 12
> thread for each disk) and its runs for 2+ hours.
> I.e 10*12=120 threads (for 10 disks)
> Small test:
> RHEL7, 32 cores, 20 GB RAM, 8 GB DN heap
> ||dfs.datanode.block.id.layout.upgrade.threads||Blocks||Disks||Time taken||
> |12|3.3 Million|1|2 minutes and 59 seconds|
> |6|3.3 Million|1|2 minutes and 35 seconds|
> |3|3.3 Million|1|2 minutes and 51 seconds|
> Tried same test twice and 95% is accurate (only a few sec difference on each
> iteration). Using 6 thread is faster than 12 thread because of its overhead.
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