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https://issues.apache.org/jira/browse/HDFS-5776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877161#comment-13877161
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Liang Xie commented on HDFS-5776:
---------------------------------
bq. Nit: This seems extraneous in the new Callable: + return null;
the "return null" is needful, since we have a "Future<Void>" definition, if we
remove the "return null", the compiler will complain:)
bq. Nit: No need of the intermediary 'instance' assignment – just assign to
'injector'?
we need, it returns a object,see Javadoc:
{code}
/**
* Creates mock object of given class or interface.
* <p>
* See examples in javadoc for {@link Mockito} class
*
* @param classToMock class or interface to mock
* @return mock object
*/
public static <T> T mock(Class<T> classToMock) {
return mock(classToMock,
withSettings().defaultAnswer(RETURNS_DEFAULTS));
}
{code}
> 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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