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From "Yu Li (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15160) Put back HFile's HDFS op latency sampling code and add metrics for monitoring
Date Sat, 27 May 2017 08:13:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16027352#comment-16027352
] 

Yu Li commented on HBASE-15160:
-------------------------------

Have checked the patch and some comments:

bq. the callers of readBlock() do not know whether the returned block is read from disk, or
comes from cache
I could see there's a {{if (cacheConf.isBlockCacheEnabled())}} check in {{HFileReaderImpl#readBlock}}
where the cached block will be returned if hit, so we could simply update the metrics outside
the if check? And with the same method we could also record the IO time of {{getMetaBlock}}
in the finally clause (if cache missed). Wdyt?

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).

> 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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