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https://issues.apache.org/jira/browse/NIFI-4715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16302649#comment-16302649
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ASF GitHub Bot commented on NIFI-4715:
--------------------------------------

GitHub user adamlamar opened a pull request:

    https://github.com/apache/nifi/pull/2361

    NIFI-4715: ListS3 produces duplicates in frequently updated buckets

    Thank you for submitting a contribution to Apache NiFi.
    
    In order to streamline the review of the contribution we ask you
    to ensure the following steps have been taken:
    
    ### For all changes:
    - [Y] Is there a JIRA ticket associated with this PR? Is it referenced 
         in the commit message?
    
    - [Y] Does your PR title start with NIFI-XXXX where XXXX is the JIRA number 
you are trying to resolve? Pay particular attention to the hyphen "-" character.
    
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You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/adamlamar/nifi NIFI-4715

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/nifi/pull/2361.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #2361
    
----
commit bcaa84bba251c3a70c27a466185f6b20863eab93
Author: Adam Lamar <adamonduty@...>
Date:   2017-12-24T03:29:02Z

    NIFI-4715: ListS3 produces duplicates in frequently updated buckets

----


> ListS3 produces duplicates in frequently updated buckets
> --------------------------------------------------------
>
>                 Key: NIFI-4715
>                 URL: https://issues.apache.org/jira/browse/NIFI-4715
>             Project: Apache NiFi
>          Issue Type: Bug
>          Components: Core Framework
>    Affects Versions: 1.2.0, 1.3.0, 1.4.0
>         Environment: All
>            Reporter: Milan Das
>         Attachments: List-S3-dup-issue.xml, screenshot-1.png
>
>
> ListS3 state is implemented using HashSet. HashSet is not thread safe. When 
> ListS3 operates in multi threaded mode, sometimes it  tries to list  same 
> file from S3 bucket.  Seems like HashSet data is getting corrupted.
> currentKeys = new HashSet<>(); // need to be implemented Thread Safe like 
> currentKeys = //ConcurrentHashMap.newKeySet();
> *{color:red}+Update+{color}*:
> This is not a HashSet issue:
> Root cause is: 
> When the file gets uploaded to S3 simultaneously  when List S3 is in progress.
> onTrigger-->  maxTimestamp is initiated as 0L.
> This is clearing keys as per the code below
> When lastModifiedTime on S3 object is same as currentTimestamp for the listed 
> key it should be skipped. As the key is cleared, it is loading the same file 
> again. 
> I think fix should be to initiate the maxTimestamp with currentTimestamp not 
> 0L.
> {code}
>  long maxTimestamp = currentTimestamp;
> {code}
> Following block is clearing keys.
> {code:title=org.apache.nifi.processors.aws.s3.ListS3.java|borderStyle=solid}
>  if (lastModified > maxTimestamp) {
>                     maxTimestamp = lastModified;
>                     currentKeys.clear();
>                     getLogger().debug("clearing keys");
>                 }
> {code}



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