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From "Arpit Agarwal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10682) Replace FsDatasetImpl object lock with a separate lock object
Date Mon, 01 Aug 2016 23:57:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15403061#comment-15403061

Arpit Agarwal commented on HDFS-10682:

Thanks for the updated patch [~vagarychen]! This is looking good. A couple of comments:
# We also need to fix other locations that are synchronizing on the FSDatasetImpl object e.g.
# Let's move the instrumentation changes to a separate Jira. We can repurpose this just for
splitting out the lock. Comments on the instrumentation changes:
## We don't need ThreadLocal or threadID-> timestamps map. We are measuring the lock held
time so we can save a timestamp just after getting the lock and another timestamp just before
releasing the lock. Then diff them with the lock held and log after releasing the lock. We
may need to use a thread local approach later if we have a read-write lock in which case there
can be multiple concurrent lock holders.
## You don't need the {{if (start == 0 || start2 == 0)}} checks. These values they can be
assumed to be correct now they are initialized in the lock class.

> Replace FsDatasetImpl object lock with a separate lock object
> -------------------------------------------------------------
>                 Key: HDFS-10682
>                 URL: https://issues.apache.org/jira/browse/HDFS-10682
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>            Reporter: Chen Liang
>            Assignee: Chen Liang
>         Attachments: HDFS-10682.001.patch, HDFS-10682.002.patch, HDFS-10682.003.patch,
HDFS-10682.004.patch, HDFS-10682.005.patch, HDFS-10682.006.patch
> Add a metric to measure the time the lock of FSDataSetImpl is held by a thread. The goal
is to expose this for users to identify operations that locks dataset for long time ("long"
in some sense) and be able to understand/reason/track the operation based on logs.

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