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From "Chen Liang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10682) Replace FsDatasetImpl object lock with a separate lock object
Date Tue, 02 Aug 2016 00:19:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15403093#comment-15403093

Chen Liang commented on HDFS-10682:

Thank you [~arpitagarwal] very much for the review! A few things I would like to clarify though:

1. by "fix the other locations", did you mean fixing places like such?:
synchronized(dataset) {
As dataset itself has been refactored with a separate lock, having this synchronized cal meanswe
would have two locks here. I have been thinking about situations like this. And I think we
need dataset to expose lock acquire and release to those callers. What do you think?

2. Regarding the ThreadLocal variables, you have a good point. But I was trying to take into
account lock acquire time and lock release time there, which requires recording time before
acquiring lock and after releasing lock and this is ThreadLocal is all about. Do you have
any comments on this? e.g. are these values worth recording?

3. And you are totally right that I don't need the equals zero checks, thanks for pointing
it out!

> 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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