Requirements: To use VSAM RLS, you must define
a single, master CF lock structure. If, however, you use the DUPLEX
attribute, you only define one CF lock structure. That is because
the structure gets created automatically into the secondary CF.
For
maximum availability, define nonvolatile lock structures. CF
lock structures enforce the protocol restrictions for VSAM RLS data
sets and maintain the record-level locks and other DFSMSdfp serialization.
Ensure that the CF lock structures have universal connectivity, so
that they are accessible from all systems in the Parallel Sysplex® that
support VSAM RLS. For system-managed duplexing, define the lock structure
as duplexed (DUPLEX (ENABLED) or DUPLEX (ALLOWED) in the CFRM policy.
For more information about system-managed lock structure duplexing,
see Recovering the CF lock structure.
The
Primary CF lock
structure is named
IGWLOCK00. Use the XCF coupling definition process to define it.
To estimate its size requirements in megabytes, use the following
formula (a megabyte is 1048576 bytes in this case):
10M * number_of_systems * lock_entry_size
where:
- 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 following table to determine the actual lock entry size for the
different MAXSYSTEM setting values:
Table 1. Effect of MAXSYSTEM
Value on Lock Table Entry SizeMAXSYSTEM Value |
Lock
Entry Size |
7 or less |
2 bytes |
>= 8 and < 24 |
4 bytes |
>= 24 and <= 32 |
8 bytes |
Table 2 shows some sample
lock allocation estimates:
Table 2. CF Lock Structure
Sizing ExamplesMAXSYSTEM Value |
Number of systems |
Total
Lock Size |
<= 7 |
2 |
64MB |
4 |
80MB |
<= 23 |
8 |
320 MB |
<default> =8 |
2 |
80 MB |
4 |
160 MB |
8 |
320 MB |
32 |
2 |
160 MB |
4 |
320 MB |
8 |
320 MB |
These lock
size estimates include the memory requirements for both
the lock table and the record-lock memory. Use these estimates as
rough initial values to help you attain a locking structure with a
desired false contention target of approximately one-half of 1% or
less. Contact your marketing representative for help in arriving at
an initial estimate that more closely matches your specific configuration.
Note: XES rounds up the number of lock entries to the next highest
power of two. For example, if you base your calculations on 2 * 10M
= 20M locks, XES allocates the structure with 32M locks.
The
primary DFSMS CF lock structure, IGWLOCK00,
has persistent connections and is a persistent structure. To delete
this structure you must use the operator command:
V SMS,SMSVSAM,FORCEDELETELOCKSTRUCTURE