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https://issues.apache.org/jira/browse/HBASE-15160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16030045#comment-16030045
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Enis Soztutar commented on HBASE-15160:
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bq. Previously the concern on readAtOffset completely make sense, but
HBASE-17917 has removed the stream lock so no more stream read when pread is
true, which makes it possible to move the updating of the metrics up to the
caller (smile).
Agreed that with the stream lock gone, we can always know when it was a pread
and when it was not from the caller. However, why do you think that updating
the metrics should be pulled up the stack? Since there are no other
synchronization points, they are equal in terms of cost. The reason I wanted to
be pushed down the stack is that in some cases (for example checksum failure)
we are doing two reads transparently to the caller. The metrics pulled up the
stack will be incorrect slightly when things like this happens. Also I want to
backport this to branch-1, so keeping the metrics update here should give us
better portability of future patches.
> Put back HFile's HDFS op latency sampling code and add metrics for monitoring
> -----------------------------------------------------------------------------
>
> Key: HBASE-15160
> URL: https://issues.apache.org/jira/browse/HBASE-15160
> Project: HBase
> Issue Type: Sub-task
> Affects Versions: 2.0.0, 1.1.2
> Reporter: Yu Li
> Assignee: Yu Li
> Priority: Critical
> Attachments: HBASE-15160.patch, HBASE-15160_v2.patch,
> HBASE-15160_v3.patch, hbase-15160_v4.patch, hbase-15160_v5.patch,
> hbase-15160_v6.patch
>
>
> In HBASE-11586 all HDFS op latency sampling code, including fsReadLatency,
> fsPreadLatency and fsWriteLatency, have been removed. There was some
> discussion about putting them back in a new JIRA but never happened.
> According to our experience, these metrics are useful to judge whether issue
> lies on HDFS when slow request occurs, so we propose to put them back in this
> JIRA, and add the metrics for monitoring as well.
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