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From Íñigo Goiri (JIRA) <j...@apache.org>
Subject [jira] [Commented] (HADOOP-16161) NetworkTopology#getWeightUsingNetworkLocation return unexpected result
Date Wed, 06 Mar 2019 17:28:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-16161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16785895#comment-16785895

Íñigo Goiri commented on HADOOP-16161:

Thanks [~hexiaoqiao] for  [^HADOOP-16161.002.patch].
Yetus is giving very weird reports but this should be fine.
Minor comments:
* Can we keep getWeightUsingNetworkLocation() static?
* Can we add a comment explaining the +2 in line 836.
* Can we add a comment explaining the topology in {{testGetWeightForDepth()}}?
* We have a lot of nodes and they are not really used for tests in {{testGetWeightForDepth()}}.

> NetworkTopology#getWeightUsingNetworkLocation return unexpected result
> ----------------------------------------------------------------------
>                 Key: HADOOP-16161
>                 URL: https://issues.apache.org/jira/browse/HADOOP-16161
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: net
>            Reporter: He Xiaoqiao
>            Assignee: He Xiaoqiao
>            Priority: Major
>         Attachments: HADOOP-16161.001.patch, HADOOP-16161.002.patch
> Consider the following scenario:
> 1. there are 4 slaves and topology like:
> Rack: /IDC/RACK1
>    hostname1
>    hostname2
> Rack: /IDC/RACK2
>    hostname3
>    hostname4
> 2. Reader from hostname1, and calculate weight between reader and [hostname1, hostname3,
hostname4] by #getWeight, and their corresponding values are [0,4,4]
> 3. Reader from client which is not in the topology, and in the same IDC but in none rack
of the topology, and calculate weight between reader and [hostname1, hostname3, hostname4]
by #getWeightUsingNetworkLocation, and their corresponding values are [2,2,2]
> 4. Other different Reader can get the similar results.
> The weight result for case #3 is obviously not the expected value, the truth is [4,4,4].
this issue may cause reader not really following arrange: local -> local rack -> remote
> After dig the detailed implement, the root cause is #getWeightUsingNetworkLocation only
calculate distance between Racks rather than hosts.
> I think we should add constant 2 to correct the weight of #getWeightUsingNetworkLocation.

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