Liang Xie created HDFS-5727:
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Summary: introduce a self-maintain io queue handling mechanism
Key: HDFS-5727
URL: https://issues.apache.org/jira/browse/HDFS-5727
Project: Hadoop HDFS
Issue Type: New Feature
Components: datanode
Affects Versions: 3.0.0
Reporter: Liang Xie
Assignee: Liang Xie
Currently the datanode read/write SLA is dfficult to be ganranteed for HBase
online requirement. One of major reasons is we don't support io priority or io
reqeust reorder inside datanode.
I proposal introducing a self-maintain io queue mechanism to handle io request
priority. Image there're lots of concurrent read/write reqeust from HBase side,
and a background datanode block scanner is running(default is every 21 days,
IIRC) just in time, then the HBase read/write 99% or 99.9% percentile latency
would be vulnerable despite we have a bg thread throttling...
the reorder stuf i have not thought clearly enough, but definitely the reorder
in the queue in the app side would beat the currently relying OS's io queue
merge.
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