Logging (LXX) Considerations and Differences

For applications that update only one CA Datacom/DB MUF and do not access any other resource managers such as VSAM, DB2, and so on, with regard to logging considerations there is no effective difference between Version 14.0 and the previous releases of CA Datacom CICS Services. But a CICS SYNCPOINT is substituted for the original LOG command. This in turn generates a LOG command to CA Datacom/DB. However, it is slightly different beginning in Version 14.0 for transactions and applications that update multiple resources such as a second CA Datacom/DB MUF, using the Log Area (LXX) for logging, because of the use of two-phase commit. Doing updates on two CA Datacom/DB MUFs or on one MUF and another resource such as VSAM or DB2, means using multiple resource managers. Therefore, the potential exists for two physical I/Os to the LXX instead of one. That is, one I/O is for the Prepare phase and one I/O is for the Commit phase. In CA Datacom CICS Services r2.6, there was only one physical I/O to the LXX, even for a two-phase commit. In CA Datacom/DB 11.0 and higher, true two-phase commit protocol was introduced which means two physical I/Os. The number of two-phase commits has been increased beginning in Version 14.0 by converting simple user log commands to SYNCPOINTs.

You should therefore consider possible performance overhead in writing more I/Os to the LXX. There may be a slight size increase required for the extra LXX records as well. Also, user issued log commands will generally produce more LXX I/Os than in releases prior to 14.0. For more information, see CICS Emergency Restart Environmental Considerations.