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https://issues.apache.org/jira/browse/HDFS-13168?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16369368#comment-16369368
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BELUGA BEHR commented on HDFS-13168:
------------------------------------

{code}
## Current Implementation

Result "org.apache.hadoop.hdfs.tools.offlineImageViewer.TestSpeed.testSpeed":
  1737.194 ±(99.9%) 19.775 ops/s [Average]
  (min, avg, max) = (1533.113, 1737.194, 1967.332), stdev = 83.729
  CI (99.9%): [1717.419, 1756.969] (assumes normal distribution)


# Run complete. Total time: 00:06:45

Benchmark                                Mode  Cnt     Score    Error  Units
offlineImageViewer.TestSpeed.testSpeed  thrpt  200  1737.194 ± 19.775  ops/s


## Patch Impelementation

Result "org.apache.hadoop.hdfs.tools.offlineImageViewer.TestSpeed.testSpeed":
  1781.301 ±(99.9%) 21.108 ops/s [Average]
  (min, avg, max) = (1407.945, 1781.301, 2020.971), stdev = 89.372
  CI (99.9%): [1760.193, 1802.409] (assumes normal distribution)


# Run complete. Total time: 00:06:45

Benchmark                                Mode  Cnt     Score    Error  Units
offlineImageViewer.TestSpeed.testSpeed  thrpt  200  1781.301 ± 21.108  ops/s
{code}

... and memory fragmentation is not really counted here of the {{LinkedList}} 
because of large heap size

> XmlImageVisitor - Prefer Array over LinkedList
> ----------------------------------------------
>
>                 Key: HDFS-13168
>                 URL: https://issues.apache.org/jira/browse/HDFS-13168
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs
>    Affects Versions: 3.0.0
>            Reporter: BELUGA BEHR
>            Priority: Minor
>         Attachments: HDFS-13168.1.patch, HDFS-13168.2.patch
>
>
> {{ArrayDeque}}
> {quote}This class is likely to be faster than Stack when used as a stack, and 
> faster than LinkedList when used as a queue.{quote}
> .. not to mention less memory fragmentation (single backing array v.s. many 
> ArrayList nodes).
> https://docs.oracle.com/javase/8/docs/api/java/util/ArrayDeque.html



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