PM73355: SLOW NETWORK TRANSFER RATES FOR MQSERIES CONNECTIONS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• MQSeries connections (or any application that tends to send
  data in large bursts) have the potential to experience low
  throughput rates to partner systems.
  
  Symptoms include:
  
  1. High number of messages per second that hit XMITQ to result
     in the latency spikes.
  
  2. SMF data (types 115 and  116 for queue managers) shows long
     PUTs, buffer pool getting full, above-normal number of pages
     per I/O.
  
  3. RMF III report shows high CPU usage in CHINIT address space
     (e.g. 60-70%) in 10-second intervals for spikes in messages
     and latency.
  
  4. RMF III report shows significant CPU delays (> 10%) for
     CHINIT.
  
  This problem can also impact bulk transfer protocols (such as
  FTP or Connect:Direct) when the network has a high rate of
  packet loss or the sending application is not getting CPU or I/O
  resources when needed.
  
  
  
  Verification steps include:
  
  1. NETSTAT ALL on the individual connections and note the
     congestion window size as well as the calculated round-trip
     time.
  
     Only the outbound connection would be affected.  If the
     remote system's IP address is y.y.y.y and the MQ listener is
     is on port nnnn, the command would be:
  
       TSO:       NETSTAT ALL (IPPORT y.y.y.y+nnnn
       OpConsole: D TCPIP,,NETSTAT,ALL,IPPORT=y.y.y.y+nnnn
  
  2. Review the smoothed round trip time (is it more than a few
     ms)?
  
  3. Are there any retransmissions on the connection? If there are
     retransmissions, it is an indication of problems outside of
     z/OS and is an issue that would need to be corrected before
     analysis can be done for whether or not the APAR applies.
     If the problem appears to be outside of z/OS, then collect a
     network sniffer trace on a shadowed switch port.
  
  4. If the NETSTAT ALL report shows congestion window size
     increases with no decreases for a MQseries connection,
     then the APAR would apply.
  

Local fix

• (None)
  
  KEYWORDS:
  MQ MQSERIES WINDOWSIZE CONGESTION WINDOW PERF PERFORMANCE
  LATENCY ROUNDTRIP RTT CHINIT XMITQ CPU DELAY TCP
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications Server   *
  *                 for z/OS Version 1 Release 13 IP             *
  ****************************************************************
  * PROBLEM DESCRIPTION: Slow network transfer rates for         *
  *                      TCPIP connections.                      *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  TCPIP connections that send data in bursts cause the senders
  congestion window to be incorrectly reduced. The reduced
  congestion window causes poor connection performance.
  In some scenarios the performance may decrease enough to
  trigger a timeout failure at an application level.
  +-------------------------------------------------------------+
  + Please check our Communications Server for OS/390 homepages +
  + for common networking tips and fixes.  The URL for these    +
  + homepages can be found in Informational APAR II11334.       +
  +-------------------------------------------------------------+
  

Problem conclusion

• TCPIP has been modified to limit congestion window reduction.
  
  * Cross Reference between External and Internal Names
  

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:

  UK82536

Modules/Macros

• EZBTCFWR EZBTCSND EZBTLFWR EZBT6FWR EZBT6LWR
  EZBT6SND TCSNDINT T6SNDINT
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R1D0 PSY UK82536

     UP12/11/15 P F211

Fix is available

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