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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-14083) libhdfs logs errors when opened FS doesn't support ByteBufferReadable
Date Mon, 11 Feb 2019 19:08:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-14083?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16765296#comment-16765296

Todd Lipcon commented on HDFS-14083:

if (errno != 0) {

this doesn't seem quite right, since there isn't a guarantee that 'readDirect' sets errno
to 0 in the case of success. It might just pick up some previously-existing value there.

Also, the handling of those static variables seems thread-unsafe. It might work OK since the
values are small enough to be naturally atomic on x86 but it seems like we might be better
off addressing the root of this issue a better way instead of throttling the error logging?

> libhdfs logs errors when opened FS doesn't support ByteBufferReadable
> ---------------------------------------------------------------------
>                 Key: HDFS-14083
>                 URL: https://issues.apache.org/jira/browse/HDFS-14083
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: native, test
>    Affects Versions: 3.0.3
>            Reporter: Pranay Singh
>            Assignee: Pranay Singh
>            Priority: Minor
>         Attachments: HADOOP-15928.001.patch, HADOOP-15928.002.patch, HDFS-14083.003.patch,
HDFS-14083.004.patch, HDFS-14083.005.patch, HDFS-14083.006.patch, HDFS-14083.007.patch, HDFS-14083.008.patch,
> Problem:
> ------------
> There is excessive error logging when a file is opened by libhdfs (DFSClient/HDFS) in
S3 environment, this issue is caused because buffered read is not supported in S3 environment,
HADOOP-14603 "S3A input stream to support ByteBufferReadable"  
> The following message is printed repeatedly in the error log/ to STDERR:
> {code}
> --------------------------------------------------------------------------------------------------
> UnsupportedOperationException: Byte-buffer read unsupported by input streamjava.lang.UnsupportedOperationException:
Byte-buffer read unsupported by input stream
>         at org.apache.hadoop.fs.FSDataInputStream.read(FSDataInputStream.java:150)
> {code}
> h3. Root cause
> After investigating the issue, it appears that the above exception is printed because
> when a file is opened via {{hdfsOpenFileImpl()}} calls {{readDirect()}} which is hitting
> exception.
> h3. Fix:
> Since the hdfs client is not initiating the byte buffered read but is happening in a
implicit manner, we should not be generating the error log during open of a file.

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