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https://issues.apache.org/jira/browse/HADOOP-18296?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18011268#comment-18011268
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ASF GitHub Bot commented on HADOOP-18296:
-----------------------------------------
steveloughran opened a new pull request, #7846:
URL: https://github.com/apache/hadoop/pull/7846
Option "fs.file.checksum.verify" disables checksum verification in local FS,
so sliced subsets of larger buffers are never returned.
Stream capability "fs.capability.vectoredio.sliced" is true if a filesystem
knows that it is returning slices of a larger buffer. This is false if a
filesystem doesn't, or against the local FS in releases which lack this feature.
Contributed by Steve Loughran
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### Description of PR
this is #7732 as cherrypicked from branch-3.4 to trunk
### How was this patch tested?
run modified common and hadoop-aws tests; full aws test in progress
### For code changes:
- [ ] Does the title or this PR starts with the corresponding JIRA issue id
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> Memory fragmentation in ChecksumFileSystem Vectored IO implementation.
> ----------------------------------------------------------------------
>
> Key: HADOOP-18296
> URL: https://issues.apache.org/jira/browse/HADOOP-18296
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: common
> Affects Versions: 3.4.0
> Reporter: Mukund Thakur
> Assignee: Steve Loughran
> Priority: Minor
> Labels: fs, pull-request-available
> Fix For: 3.4.2
>
>
> As we have implemented merging of ranges in the ChecksumFSInputChecker
> implementation of vectored IO api, it can lead to memory fragmentation. Let
> me explain by example.
>
> Suppose client requests for 3 ranges.
> 0-500, 700-1000 and 1200-1500.
> Now because of merging, all the above ranges will get merged into one and we
> will allocate a big byte buffer of 0-1500 size but return sliced byte buffers
> for the desired ranges.
> Now once the client is done reading all the ranges, it will only be able to
> free the memory for requested ranges and memory of the gaps will never be
> released for eg here (500-700 and 1000-1200).
>
> Note this only happens for direct byte buffers.
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