Performance parameters in CICS

System design considerations for CICS® with DBCTL are similar to the design considerations that applied to local DL/I. For example, do not allow excessive database accesses or updates in a single UOW. However, some system design considerations are specific to CICS with DBCTL.

The fact that DBCTL is structured to have one TCB per thread is an additional consideration for CICS. This allows more concurrent processing, but you need to specify minimum and maximum numbers of threads that are consistent with the needs of your system. For more information, see Specifying numbers of threads.

The storage specified in CICS system initialization parameters DSALIM and EDSALIM is used for different resources in a CICS-DBCTL environment.
  • DSALIM is used to specify the upper limit of the total amount of storage within which CICS can allocate the individual DSAs below the 16 MB line.
  • EDSALIM is used to specify the upper limit of the total amount of storage within which CICS can allocate the individual EDSAs above 16 MB but below 2 GB.
Local uses DSA storage for PSB and DMB pools, but with DBCTL, these blocks are stored outside CICS. Instead, you need to allow for the storage DBCTL needs in CICS for DRA code when specifying DSALIM and EDSALIM. This storage is allocated in the CICS region, but not from DSA or EDSA storage. For information about specifying DSALIM and EDSALIM, see CICS dynamic storage areas..

Using single-phase commit

CICS can use single-phase commit instead of two-phase commit when, for a specific UOW, DBCTL is the only recoverable resource used. Using single-phase commit in these circumstances improves CICS performance with DBCTL by eliminating unnecessary logging, cutting restart time, decreasing transaction cost, and improving response time in both CICS and DBCTL. For information on using single-phase commit, see Increasing efficiency: single-update and read-only protocols.