A lock structure sizing example

Suppose a Parallel Sysplex® has a MAXSYSTEM setting of 3, with two systems currently connected to the CF. You could use the initial sizing formula to estimate its initial size, as shown below:

Initial Lock Structure Size = 10M * 2 * 2

where:

number_of_systems = 2
lock_entry_size = 2 bytes

This yields an initial lock structure size of 40MB. However, to maximize the lock table space itself, you should size it with a number that is a power of two. In this case, the initial total lock size could be set at either 32 or 64 MB.

For the purpose of this example, we select 32 MB as the initial lock structure size. We then run for a while before determining the rate of false contentions. Assuming that this false contention rate is 1.5%, and that we have a target false contention rate of 0.5%, we can then use the following formula to modify the lock structure size:

Minimum Lock Structure Size = 1.5 * 32MB / 0.5

where:

1.5 is the measured false contention rate of 1.5%
32 MB is the specified lock structure size
0.5 is the target false contention rate of 0.5%

The adjusted size should now be 96 MB. However, because this needs to be expressed as a power of two, unless we actually select a value of at least 128 MB, it is unlikely that we will find that the false contention rate meets or exceeds our target of 0.5%.

In this example, the Parallel Sysplex would run better with a larger lock structure size than initially allocated. On the other hand, had the monitored false contention rate been less than an initial target value of 0.5%, it would not mean that we were wasting CF storage by having it allocated to the lock structure. In fact, although a false contention rate of 0.1% is not feasible in many cases, it is still ideal, assuming that it can be achieved with a reasonable amount of CF memory.