[jira] [Work logged] (HADOOP-17408) Optimize NetworkTopology while sorting of block locations

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-17408?focusedWorklogId=519789&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-519789 ]

ASF GitHub Bot logged work on HADOOP-17408:
-------------------------------------------

                Author: ASF GitHub Bot
            Created on: 03/Dec/20 17:48
            Start Date: 03/Dec/20 17:48
    Worklog Time Spent: 10m 
      Work Description: amahussein opened a new pull request #2514:
URL: https://github.com/apache/hadoop/pull/2514


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Issue Time Tracking
-------------------

            Worklog Id:     (was: 519789)
    Remaining Estimate: 0h
            Time Spent: 10m

> Optimize NetworkTopology while sorting of block locations
> ---------------------------------------------------------
>
>                 Key: HADOOP-17408
>                 URL: https://issues.apache.org/jira/browse/HADOOP-17408
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: common, net
>            Reporter: Ahmed Hussein
>            Assignee: Ahmed Hussein
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> In {{NetworkTopology}}, I noticed that there are some hanging fruits to improve the performance.
> Inside {{sortByDistance}}, collections.shuffle is performed on the list before calling {{secondarySort}}.
> {code:java}
> Collections.shuffle(list, r);
> if (secondarySort != null) {
>   secondarySort.accept(list);
> }
> {code}
> However, in different call sites, {{collections.shuffle}} is passed as the secondarySort to {{sortByDistance}}. This means that the shuffle is executed twice on each list.
> Also, logic wise, it is useless to shuffle before applying a tie breaker which might make the shuffle work obsolete.
> In addition, [~daryn] reported that:
> * topology is unnecessarily locking/unlocking to calculate the distance for every node
> * shuffling uses a seeded Random, instead of ThreadLocalRandom, which is heavily synchronized



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