IRLM storage size

For data sharing, plan for additional IRLM storage to accommodate data sharing-specific locks called P-locks.

Tip: You can use the coupling facility structure sizer (CFSizer) tool to help you calculate CF structure storage sizes for Db2 data sharing. For more information, see The CFSizer tool .

P-locks are held on open page sets and on database descriptors (DBDs), skeleton cursor tables (SKCTs), and skeleton package tables (SKPTs). Unlike transaction locks, storage for P-locks is held even when no transaction activity exists; therefore they consume storage even with no transaction activity.

Plan also for the extra storage that IRLM needs to build retained locks in case other members fail. The following table shows the variables that you need to take into account.

Table 1. Variables that are used to estimate additional IRLM storage
Variable Description Calculation
X P-locks 1 N = (MAX_OPEN_DATA_SETS × 500)

X = (N + (N × .40)
Y Ability to hold update-retained locks for a failed member Depends on the update intensity of the workload. Start with the following:

Y = .25(X)(X)
Note:

1. The formula is based on the assumption that more than one P-lock might be held on a page set occasionally (such as for castout activity), and an estimate of about 40% for P-locks on the EDM pool objects and for short-lived page P-locks. If you know that the EDM pool has relatively few objects in it, you can use a lower percentage for that value. Estimate the maximum number of open data sets or use the value that is specified for the subsystem parameter DSMAX.