[
https://issues.apache.org/jira/browse/HADOOP-3914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12620686#action_12620686
]
Raghu Angadi commented on HADOOP-3914:
--------------------------------------
Yes, location has changed, but I am still trying to see how that gets
triggered. I see two related but different issues :
# DFSClient is triggering an IOException that it could ignore. It should not
trigger these exceptions unnecessarily, of course.
#* we could fix this as part of this jira.
# An exception that it expected to be completely internal to DFSClient is
breaking some other application.
#* I am surprised that this happens, would surely like to more. we may not
able to fix this.
#* More importantly legitimate exceptions could break these applications.
> checksumOk implementation in DFSClient can break applications
> -------------------------------------------------------------
>
> Key: HADOOP-3914
> URL: https://issues.apache.org/jira/browse/HADOOP-3914
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.17.1
> Reporter: Christian Kunz
>
> One of our non-map-reduce applications (written in C and using libhdfs to
> access dfs) stopped working after switch from 0.16 to 0.17.
> The problem was finally traced down to failures in checksumOk.
> I would assume, the purpose of checksumOk is for a DfsClient to indicate to a
> sending Datanode that the checksum of the received block is okay. This must
> be useful in the replication pipeline.
> How checksumOk is implemented is that any IOException is caught and ignored,
> probably because it is not essential for the client that the message is
> successful.
> But it proved fatal for our application because this application links in a
> 3rd-party library which seems to catch socket exceptions before libhdfs.
> Why was there an Exception? In our case the application reads a file into the
> local buffer of the DFSInputStream large enough to hold all data, the
> application reads to the end and the checksumOK is sent successfully at that
> time. But then the application does some other stuff and comes back to
> re-read the file (still open). It is then when it calls checksumOk again and
> crashes.
> It can easily be avoided by adding a Boolean making sure that checksumOk is
> called exactly once when EOS is encountered. Redundant calls to checksumOk do
> not seem to make sense anyhow.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
