IC99372: A WEBSPHERE MQ FILE TRANSFER EDITION V7.0.4 MESSAGE-TO-FILE TRANSFER OVER SFTP FILE SERVER ENTERS RECOVERY

WebSphere MQ File Transfer Edition V7.0 Fix Pack 7.0.4.5

APAR status

• Closed as program error.

Error description

• When performing a message-to-file transfer using the SFTP
  protocol to a file server, the transfer enters recovery and the
  SSH server log reports the following error:
  
  SSH_MSG_DISCONNECT: 2 Received data for nonexistent channel 0.
  
  This error message is also output in the trace logs by the
  WebSphere MQ File Transfer Edition protocol bridge agent when
  tracing for the agent has been enabled.
  
  The exception can occur multiple times during the transfer, and
  each time it results in the WebSphere MQ File Transfer Edition
  protocol bridge agent performing recovery processing on the
  transfer.
  

Local fix

• Configure the WebSphere MQ File Transfer Edition agents such
  that they are able to transfer all the data for the final file
  within one transfer chunk.
  
  In order to do this, you need to know the maximum size of the
  file being transferred, which is the total size of the message
  data on the source queue.
  
  This is configured using three agent properties, which are
  multiplied together to determine the maximum chunk size:
  
    "agentChunkSize" defaulting to 262144 bytes (256 KB)
    "agentFrameSize" defaulting to 5
    "agentWindowSize" defaulting to 10
  
  These values multiplied together give you the upper JVM memory
  limit used for a specific transfer, which with the default
  values is 12.5 MB.
  
  
  If you increase these values (eg. change the "agentChunkSize"
  agent property) so that the multiplication of the three values
  gives a value which is greater than the transferred file size,
  then the system will circumvent the issue.
  

Problem summary

• ****************************************************************
  USERS AFFECTED:
  This issue affects users of the WebSphere MQ File Transfer
  Edition protocol bridge agent who perform file transfers to or
  from file servers using the SFTP protocol.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM SUMMARY:
  WebSphere MQ File Transfer Edition protocol bridge agents can
  perform file transfers to and from a file server using the SFTP
  protocol.
  
  When performing a file transfer to an SFTP file server, file
  data that arrived at the protocol bridge agent, and read off the
  agent's SYSTEM.FTE.DATA. queue, was queued internally and later
  processed by a thread dedicated to writing the file data to the
  file server.
  
  The first thread that was created to process the initial file
  data was responsible for establishing a connection to the SFTP
  file server and opening an OutputStream to the destination file
  to which the file data could be written. This thread then writes
  the queued file data to the OutputStream. Once all the data that
  has been received by the protocol bridge agent had been written
  and the internal queue became empty, the thread waited for a
  short period of time for more data to arrive. If no more data
  arrived within that period of time, for example because the
  WebSphere MQ File Transfer Edition source agent is under load,
  the thread processing the queue was terminated.
  
  When more file data was then later received by the WebSphere MQ
  File Transfer Edition protocol bridge agent, sent from the
  WebSphere MQ File Transfer Edition source agent for the
  transfer, a new thread was started to process the file data.
  This new thread, used the cached connection and OutputStream
  that was previously created by the first thread. The fact that
  this new thread reused the OutputStream to write the new file
  data caused the SFTP file server to throw the exception outlined
  in the Problem Description section of this APAR. This resulted
  in the agent closing the connection to the SFTP file server, put
  the transfer into recovery and attempt to restart the transfer
  from the last checkpoint.
  
  The same issue can occur when transferring a file from an SFTP
  file server as the InputStream could have been shared across
  multiple threads.
  

Problem conclusion

• The WebSphere MQ File Transfer Edition protocol bridge agent
  code has been updated such that the same thread is used when
  writing and reading file data on a file server when using the
  SFTP protocol.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v7.0       7.0.4.5
  v7.5       7.5.0.5
  
  The latest available maintenance can be obtained from
  'WebSphere MQ Recommended Fixes'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
  
  If the maintenance level is not yet available information on
  its planned availability can be found in 'WebSphere MQ
  Planned Maintenance Release Dates'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
  ---------------------------------------------------------------
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  WMQ FILE TRANSF

• Fixed component ID

  5724R1000

Applicable component levels

• R704 PSY

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