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https://issues.apache.org/jira/browse/HDFS-6293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13983095#comment-13983095
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Kihwal Lee commented on HDFS-6293:
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Outputting in the new XML format is fast and consumes little memory because it
is essentially dumping what is in the image in order. It does not provide
readily usable directory/file information as it used to in pre-2.4/protobuf
versions.
Using something like the "ls -l" format or any custom visitor for dumping file
system tree will require loading of all inodes upfront and linking them
afterwards. This requires considerably larger amount of memory. The smallest
footprint will be similar to NN's without triplets. It is clearly
unacceptable. Reducing memory consumption at the price of considerably longer
processing time is also unacceptable.
> Issues with OIV processing PB-based fsimages
> --------------------------------------------
>
> Key: HDFS-6293
> URL: https://issues.apache.org/jira/browse/HDFS-6293
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.4.0
> Reporter: Kihwal Lee
> Priority: Blocker
>
> There are issues with OIV when processing fsimages in protobuf.
> Due to the internal layout changes introduced by the protobuf-based fsimage,
> OIV consumes excessive amount of memory. We have tested with a fsimage with
> about 140M files/directories. The peak heap usage when processing this image
> in pre-protobuf (i.e. pre-2.4.0) format was about 350MB. After converting
> the image to the protobuf format on 2.4.0, OIV would OOM even with 80GB of
> heap (max new size was 1GB). It should be possible to process any image with
> the default heap size of 1.5GB.
> Another issue is the complete change of format/content in OIV's XML output.
> I also noticed that the secret manager section has no tokens while there were
> unexpired tokens in the original image (pre-2.4.0). I did not check whether
> they were also missing in the new pb fsimage.
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