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https://issues.apache.org/jira/browse/HDFS-13428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16435793#comment-16435793
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Íñigo Goiri commented on HDFS-13428:
------------------------------------

Thanks [~belugabehr] for the pointer; the second answer with the graphs is 
specially interesting.
I mostly track RBF changes but let me know if you need help pushing these fixes 
anywhere else.
There are a bunch of places in RBF where we could use some optimizations.

> RBF: Remove LinkedList From StateStoreFileImpl.java
> ---------------------------------------------------
>
>                 Key: HDFS-13428
>                 URL: https://issues.apache.org/jira/browse/HDFS-13428
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: federation
>    Affects Versions: 3.0.1
>            Reporter: BELUGA BEHR
>            Assignee: BELUGA BEHR
>            Priority: Trivial
>             Fix For: 2.10.0, 3.2.0, 3.1.1, 2.9.2, 3.0.4
>
>         Attachments: HDFS-13428.1.patch
>
>
> Replace {{LinkedList}} with {{ArrayList}} implementation in the 
> StateStoreFileImpl class.  This is especially advantageous because we can 
> pre-allocate the internal array before a copy occurs.  {{ArrayList}} is 
> faster for iterations and requires less memory than {{LinkedList}}.
> {code:java}
>   protected List<String> getChildren(String path) {
>     List<String> ret = new LinkedList<>();
>     File dir = new File(path);
>     File[] files = dir.listFiles();
>     if (files != null) {
>       for (File file : files) {
>         String filename = file.getName();
>         ret.add(filename);
>       }
>     }
>     return ret;
>   }
> {code}



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