Karthik Palanisamy created HDFS-15610:
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Summary: Reduce datanode hardlink thread
Key: HDFS-15610
URL: https://issues.apache.org/jira/browse/HDFS-15610
Project: Hadoop HDFS
Issue Type: Bug
Components: datanode
Affects Versions: 3.1.4, 3.0.0
Reporter: Karthik Palanisamy
Assignee: Karthik Palanisamy
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.
||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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