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https://issues.apache.org/jira/browse/HDFS-5776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13878459#comment-13878459
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Liang Xie commented on HDFS-5776:
---------------------------------
Added a bit codes into YCSB to get 99.9thPercentile latency, here is the result:
dfs.dfsclient.hedged.read.threshold.millis=100ms:
{quote}
[READ], 95thPercentileLatency(us), 115973
[READ], 99thPercentileLatency(us), 124829
[READ], 99.9thPercentileLatency(us), 217892
{quote}
dfs.dfsclient.hedged.read.threshold.millis=600000ms(this's equals to disable
hedged read feature, since my test duration is 600s):
{quote}
[READ], 95thPercentileLatency(us), 149355
[READ], 99thPercentileLatency(us), 256987
[READ], 99.9thPercentileLatency(us), 418950
{quote}
In practice, maybe we should set the threshold equals to 95/99th percentile
latency, here just a test to make the difference more obviously...
> Support 'hedged' reads in DFSClient
> -----------------------------------
>
> Key: HDFS-5776
> URL: https://issues.apache.org/jira/browse/HDFS-5776
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 3.0.0
> Reporter: Liang Xie
> Assignee: Liang Xie
> Attachments: HDFS-5776-v2.txt, HDFS-5776-v3.txt, HDFS-5776-v4.txt,
> HDFS-5776-v5.txt, HDFS-5776.txt
>
>
> This is a placeholder of hdfs related stuff backport from
> https://issues.apache.org/jira/browse/HBASE-7509
> The quorum read ability should be helpful especially to optimize read outliers
> we can utilize "dfs.dfsclient.quorum.read.threshold.millis" &
> "dfs.dfsclient.quorum.read.threadpool.size" to enable/disable the hedged read
> ability from client side(e.g. HBase), and by using DFSQuorumReadMetrics, we
> could export the interested metric valus into client system(e.g. HBase's
> regionserver metric).
> The core logic is in pread code path, we decide to goto the original
> fetchBlockByteRange or the new introduced fetchBlockByteRangeSpeculative per
> the above config items.
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