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.
