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https://issues.apache.org/jira/browse/HADOOP-4298?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12635833#action_12635833
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Pete Wyckoff commented on HADOOP-4298:
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bq. if (fh->sizeBuffer == 0 || offset < fh->startOffset || offset >=
(fh->startOffset + fh->sizeBuffer))
I think this is correct. it's just very conservative: if there's any data in
the current buffer that can satisfy even 1 byte of the current request, then
use that data before refilling the buffer. The next call to read would then
trigger offset > fh->startOffset.
This of course means that fuse-dfs is often returning less than the requested
number of bytes. Is this a problem for your application?
pete
> File corruption when reading with fuse-dfs
> ------------------------------------------
>
> Key: HADOOP-4298
> URL: https://issues.apache.org/jira/browse/HADOOP-4298
> Project: Hadoop Core
> Issue Type: Bug
> Components: contrib/fuse-dfs
> Affects Versions: 0.18.1
> Environment: CentOs 4.6 final; kernel 2.6.9-67.ELsmp; FUSE 2.7.4;
> hadoop 0.18.1; 64-bit
> I hand-altered the fuse-dfs makefile to use 64-bit instead of the hardcoded
> -m32.
> Reporter: Brian Bockelman
> Priority: Critical
> Fix For: 0.18.2
>
>
> I pulled a 5GB data file into Hadoop using the following command:
> hadoop fs -put /scratch/886B9B3D-6A85-DD11-A9AB-000423D6CA6E.root
> /user/brian/testfile
> I have HDFS mounted in /mnt/hadoop using fuse-dfs.
> However, when I try to md5sum the file in place (md5sum /mnt/hadoop) or copy
> the file back to local disk using "cp" then md5sum it, the checksum is
> incorrect.
> When I pull the file using normal hadoop means (hadoop fs -get
> /user/brian/testfile /scratch), the md5sum is correct.
> When I repeat the test with a smaller file (512MB, on the theory that there
> is a problem with some 2GB limit somewhere), the problem remains.
> When I repeat the test, the md5sum is consistently wrong - i.e., some part of
> the corruption is deterministic, and not the apparent fault of a bad disk.
> CentOs 4.6 is, unfortunately, not the apparent culprit. When checking on
> CentOs 5.x, I could recreate the corruption issue. The second node was also
> a 64-bit compile and CentOs 5.2 (`uname -r` returns 2.6.18-92.1.10.el5).
> Thanks for looking into this,
> Brian
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