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