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https://issues.apache.org/jira/browse/HADOOP-17408?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jim Brennan resolved HADOOP-17408.
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Fix Version/s: 3.4.0
3.3.1
Resolution: Fixed
Thanks for the contribution [~ahussein] and [~daryn]! I have committed this to
trunk and branch-3.3.
The patch does not apply cleanly to branch-3.2 or earlier. Please provide a
patch for 3.2 if desired.
> 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
> Labels: pull-request-available
> Fix For: 3.3.1, 3.4.0
>
> Time Spent: 1h 50m
> 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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