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From "Dan Hecht (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11529) libHDFS still does not return appropriate error information in many cases
Date Mon, 20 Mar 2017 21:31:41 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11529?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15933605#comment-15933605
] 

Dan Hecht commented on HDFS-11529:
----------------------------------

Hi [~sailesh], it'd be good to document the memory ownership/lifetime of the strings returned
by the two new functions hdfGetLastException*(). i.e. the caller doesn't know from the description
whether:
1) it needs to free the memory returned. i.e. is the string copied and ownership passed to
the caller?
2) if not copied by libhdfs, when does the returned string become invalid?
Also, in the documentation comment, maybe be more specific about what "on this thread" means.

> libHDFS still does not return appropriate error information in many cases
> -------------------------------------------------------------------------
>
>                 Key: HDFS-11529
>                 URL: https://issues.apache.org/jira/browse/HDFS-11529
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: libhdfs
>    Affects Versions: 2.6.0
>            Reporter: Sailesh Mukil
>            Assignee: Sailesh Mukil
>            Priority: Critical
>              Labels: errorhandling, libhdfs
>         Attachments: HDFS-11529.000.patch
>
>
> libHDFS uses a table to compare exceptions against and returns a corresponding error
code to the application in case of an error.
> However, this table is manually populated and many times is disremembered when new exceptions
are added.
> This causes libHDFS to return EINTERNAL (or Unknown Error(255)) whenever these exceptions
are hit. These are some examples of exceptions that have been observed on an Error(255):
> org.apache.hadoop.ipc.StandbyException (Operation category WRITE is not supported in
state standby)
> java.io.EOFException: Cannot seek after EOF
> javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: No valid
credentials provided (Mechanism level: Failed to find any Kerberos tgt)
> It is of course not possible to have an error code for each and every type of exception,
so one suggestion of how this can be addressed is by having a call such as hdfsGetLastException()
that would return the last exception that a libHDFS thread encountered. This way, an application
may choose to call hdfsGetLastException() if it receives EINTERNAL.
> We can make use of the Thread Local Storage to store this information. Also, this makes
sure that the current functionality is preserved.
> This is a follow up from HDFS-4997.



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