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https://issues.apache.org/jira/browse/HDFS-5776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877255#comment-13877255
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Liang Xie commented on HDFS-5776:
---------------------------------
bq. For sure this will always trigger though the number of futures ==
numHedgedReads (should futures == numHedgedReads + 1 to be sure?)
There's no guarantee about that, we cann't predict the detailed numHedgedReads
count against futures size, there's no direct corelation.
{quote}
You need the below new log?
+ DFSClient.LOG.warn("Could not obtain block " + block + errMsg
+ + ". Throw a BlockMissingException");
{quote}
yes, it would be better if we have it once diagnoise sth.
bq. Make the above log message match the content of the BlockMissingException
so it easier connecting the two emissions (Later in the patch you actually do
this).
done
> 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.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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