XCOM Data Transport uses two communication types: user data transfer and "meta-transfers" for queuing and administrative functions. Initially, only SNA protocol was supported for meta-transfers, which was robust but required complex configuration. XCOM Data Transport for z/OS 3.1 added TCP/IP support for meta-transfers, simplifying network configuration and enabling communication with new partners without pre-definition.
Introducing the XCOM PLEXQ Feature
As part of XCOM Data Transport for z/OS, we’ve added a third intra-communication option: the XCOM PLEXQ feature. PLEXQ can be used to perform meta-transfers (e.g. TYPE=SCHEDULE, TYPE=INQUIRE, TYPE=HISTORY, etc.) between all XCOM instances running on the same z/OS SYSPLEX. The PLEXQ protocol can be used instead of TCP/IP or SNA for inter-address space communication between XCOM address spaces.
The PLEXQ feature uses IBM z/OS Sysplex Signalling Services to communicate between XCOM address spaces. Any XCOM address space running on the same SYSPLEX can perform meta-transfers using a PLEXQ connection.
In our labs at Broadcom, using PLEXQ for communications in XCOM has shown to use up to 80% less virtual storage than TCP/IP to perform the same meta-transfer operations. CPU usage was also seen to be reduced by comparison.
However, the PLEXQ feature provides more benefits than simply using less system resources. It also provides the ability to group or cluster XCOM servers together so that they can then be addressed as a single entity for initiating transfer requests or inquiring about the statuses of those transfers.
This offers an additional advantage by creating a high availability environment for scheduling transfers. For example, individual servers participating in a PLEXQ group can be stopped and started individually without impacting the ability to schedule new transfer requests to a given PLEXQ group.
Setting up the PLEXQ Feature
Setting up and using PLEXQ for meta-transfer communication is easy. An XCOM server running on a z/OS SYSPLEX can connect to a PLEXQ GROUP by specifying the PLEXQ= parameter during startup. A server can participate in up to eight PLEXQ GROUPs. In addition, a server can dynamically JOIN and LEAVE a PLEXQ GROUP using XCOM’s PLEXQ operator command. This provides an easy method of modifying an active server’s PLEXQ participation without requiring a restart.
An XCOM server can participate in one to eight PLEXQ groups simultaneously. An XCOMJOB invocation can participate in only one PLEXQ group at a time. To do this, the following format of the PLEXQ parameter is used:
PLEXQ=(GROUP1, GROUP2, GROUP3, GROUP4, GROUP5, GROUP6,GROUP7)
PLEXQ GROUP names can be up to eight characters long.
Multiple servers can reference the same group name. In that case, the servers which are connected to the same group are treated as a single entity when scheduling transfers, inquiring on transfer status, or retrieving XCOM history records using the group name.
To perform a meta-transfer over PLEXQ, the XCOMJOB utility is invoked using the STCPLEXQ= parameter. The value of this parameter must reference a PLEXQ GROUP name that already has an active XCOM server in it.
A marquee function of the PLEXQ feature is that of evenly distributing TYPE=SCHEDULE requests among the servers which are participating in the PLEXQ GROUP. The servers participating in a GROUP are polled to determine their workloads. The results of that polling are used to select the least busy server to receive each new transfer request.
The identifying information for that server is logged and, if there is an XCOMINQ DD active in the XCOMJOB step, the unique identifying information is included as part of the record in the XCOMINQ file. When the TYPE=INQUIRE is run using that XCOMINQ file, inquiries for specific transfer status are automatically routed to the server which processed the transfer.
For TYPE=HISTORY requests routed to a PLEXQ GROUP, the history information from all participating servers is returned to the XCOMJOB step. This provides a means to retrieve multiple
The PLEXQ feature enhances the use and management of XCOM server environments. For more information, consult the CA XCOM Data Transport for z/OS documentation suite.