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https://issues.apache.org/jira/browse/HDFS-4461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13568901#comment-13568901
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Suresh Srinivas commented on HDFS-4461:
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bq. This has been causing out-of-memory conditions for users who pick such long
volume paths.
I doubt that the directory scanner is the cause of OOM error. It is probably
happening due to some other issue. How many blocks per storage directory do you
have, when OOME happened?
bq. here's a before vs. after picture of a memory analysis. you can see that in
the "after" picture, we are no longer storing the path prefix twice per block
in the ScanInfo class
I have hard time understanding the picture. How many bytes are we saving per
ScanInfo?
> DirectoryScanner: volume path prefix takes up memory for every block that is
> scanned
> -------------------------------------------------------------------------------------
>
> Key: HDFS-4461
> URL: https://issues.apache.org/jira/browse/HDFS-4461
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.0.3-alpha
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Priority: Minor
> Attachments: HDFS-4461.002.patch, HDFS-4461.003.patch,
> memory-analysis.png
>
>
> In the {{DirectoryScanner}}, we create a class {{ScanInfo}} for every block.
> This object contains two File objects-- one for the metadata file, and one
> for the block file. Since those File objects contain full paths, users who
> pick a lengthly path for their volume roots will end up using an extra
> N_blocks * path_prefix bytes per block scanned. We also don't really need to
> store File objects-- storing strings and then creating File objects as needed
> would be cheaper. This has been causing out-of-memory conditions for users
> who pick such long volume paths.
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