XCOM z/OS upgrade to 12.0.3 receive file error XCOMU0492E

Products

• XCOM Data Transport - z/OS
• XCOM Data Transport
• XCOM Data Transport - Linux PC

Issue/Introduction

On a mainframe (z/OS) system that runs the older XCOM maintenance level 12.0.1,  a daily job does a receive of a large file from a midrange XCOM partner.

After XCOM for z/OS upgrade to maintenance level 12.0.3, the same job fails with:
XCOMU0492E MAXRECLEN EXCEEDS LIMIT FOR RECORD PACKING

After backing out to the older Level 12.0.1 the same job runs successfully again.
What could be the root cause?

Environment

XCOM™ Data Transport® for z/OS 12.0
XCOM™ Data Transport® for UNIX/Linux

Cause

Per the message from the Unix/Linux XCOM partner server, this problem relates to record packing.

There are 2 parts to the root cause for this particular scenario:

1. To use record packing requires PACK=LENGTH to be set.
   There was a post 12.0.1 PTF LU10772 corrected by LU12205 where the default for PACK changed from NO to LENGTH and it also became a GLOBAL parameter.
   In this scenario:
   Under 12.0.1 PACK was not being set and was defaulting to NO i.e. record packing not used.
   Under 12.0.3 doing the same will cause the new default value of LENGTH to be used i.e. use record packing.
   
   
2. When record packing is used, per the MAXPACK doc page, there is negotiation with the XCOM partner.
   "If the MAXPACK value or its equivalent on the partner side does not match the value on the local side, the value is negotiated downward."
   The current XCOM for UNIX/Linux and Windows platforms support a maximum packing length of 31744 (MAXRECLEN is the equivalent parameter).
   If the LRECL of the z/OS data set used in a send/receive transfer is larger than than 31744, the XCOM Linux and Windows platforms reject the transfer request with packing.
   Therefore a similar error could also occur on Windows: XCOMN0492E MAXRECLEN exceeds limit for record packing.

Resolution

To maintain the same "no record packing" behaviour under 12.0.3 explicitly set PACK=NO in 12.0.3 in one of:

• The SYSIN01 parameters for the transfer.
• The TYPE=DEST member used for the partner, if any.
• Globally in the TYPE=CONFIG member (or DFLTAB if used).

Additional Information

Using record packing with PACK=LENGTH is normally better for performance especially for large files.
However even if packing with a value of 31744 bytes could be used for data sets with LRECL bigger than 31744, the performance would rather degrade anyway. Therefore disabling record packing for such failing transfers is a good thing.

If record packing is wanting to be used for z/OS to UNIX/Linux or Windows transfers and unresolvable problems occur please create a new XCOM support case on the Broadcom Support Portal and provide this information in addition to the XCOM for z/OS log:

• The partner OS type and version.
• The exact XCOM version being used with this command: xcomqm -r
• A copy of the xcom.glb file (from $XCOM_HOME/config or %XCOM_HOME%\config)