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https://issues.apache.org/jira/browse/HBASE-25524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17335785#comment-17335785
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Sean Busbey commented on HBASE-25524:
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If we want the ability to confirm that a RS _can_ do SCR independent of the
specific regions it is hosting then I think we need to use a canary file. I
think #2 above is the only practical way to do that. Presumably we only need to
do this once per RS process.
I don't think it matters that later readings of hfiles might not have a local
block to use for a SCR; that notion is captured in locality and scr metrics.
After writing the canary file I don't see a straight forward way to check that
HDFS wrote the first block locally, but we can use the FSDataInputStreamWrapper
we maintain to read the file and then check if the read happened via SCR / zero
copy
> Region Servers should give some indication that short-circuit reads are
> configured properly and working
> -------------------------------------------------------------------------------------------------------
>
> Key: HBASE-25524
> URL: https://issues.apache.org/jira/browse/HBASE-25524
> Project: HBase
> Issue Type: Improvement
> Components: Performance, regionserver, Usability
> Affects Versions: 3.0.0-alpha-1, 2.3.0, 2.4.0
> Reporter: Nick Dimiduk
> Assignee: Rahul Kumar
> Priority: Major
>
> Going through the exercise of confirming short-circuit reads turns out to be
> quite a chore. 2.3.0 added a new metric, but metrics only get tickled when
> there's traffic that happens to use the feature. This is not very convenient
> for an operator who has taken a cluster out of service for maintenance.
> It would be nice if the rs process could perform some test and emitted some
> confirmation of the status of this otherwise transparent feature. After
> confirmation, it could light up a boolean metric value and/or add mention of
> it to the info page.
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