Lock-structure sizing

You define the coupling facility lock structure, IGWLOCK00, in the CFRM policy, using the IXCMIAPU utility. The following formula is for estimating the size of IGWLOCK00 (in megabytes) for VSAM RLS. You can use this formula and then add additional space for the extra locking activity by batch jobs that use DFSMStvs.

10 MB * number_of_systems * lock_entry_size

In the formula, the variables have these values:

number_of_systems: Is the number of systems in the Parallel Sysplex®.
lock_entry_size: Is the size of each lock entry. This value depends on the MAXSYSTEM value that is specified to the IXCL1DSU couple-data-set format utility.

Use the information in Table 1 to determine the actual lock-entry size for different MAXSYSTEM values.

Table 1. Effect of MAXSYSTEM value on lock-table-entry size
MAXSYSTEM value	Lock-entry size
7 or fewer	2 bytes
> = 8 and < 24	4 bytes
> = 24 and < 56	8 bytes

Table 2 shows some sample lock-allocation estimates.

Table 2. Lock-allocation estimates
MAXSYSTEM value	Number of systems	Total lock-structure size (MB)
< = 7	2	40
< = 7	4	80
default = 8	2	80
	4	160
	8	320
32	2	160
	4	320
	8	320

Use these estimates as rough initial values. Other factors influence the size of the lock structure, such as false contentions and retained locks.

Related reading:

For more information about the sizing of the lock structure, see z/OS DFSMSdfp Storage Administration.
For more information about the MAXSYSTEM parameter, see z/OS MVS Setting Up a Sysplex.