Operands related to shared memory

87) pd_shmpool_attribute = free | fixed

Specifies whether to fix the shared memory used by the HiRDB unit controller in memory. Note that the AIX 5L version of HiRDB(32-bit mode) does not support fixing of the shared memory, and therefore specification of fixed for this operand is invalid.

free:: Do not fix the shared memory in memory. Depending on the size of the real memory, another page of shared memory may be created, affecting performance adversely.

fixed:: Fix the shared memory in memory.

Advantage: Fixing the shared memory to be used by the HiRDB in the memory ("fixed" specified) prevents shared memory paging, thus improving the access performance to the shared memory.

Specification guidelines: Whether or not the shared memory is to be fixed should be based on the computed shared memory size and the real memory size of the server machine. Because there is a limit to the amount of memory that can be fixed for the HiRDB, fixing too much shared memory may cause frequent paging of other types of memory. How much real memory there is and the amount of memory to be occupied by the shared memory pool need to be carefully evaluated.; For the formula for computing the shared memory sizes to be used by the unit controller and individual servers, see the HiRDB Version 8 Installation and Design Guide.; For the formula for computing the shared memory sizes to be used by the unit controller and individual servers, see the HiRDB Version 8 Installation and Design Guide.

Notes

The following notes apply to the specification of fixed in the AIX 5L version:

Set operating system parameters for the OS. If the applicable operating system parameters are not set, this operand is ignored. For details about the operating system parameters to be set, see Specifying parameters unique to AIX 5L in the HiRDB Version 8 Installation and Design Guide.
Set the server machine's memory and the VMM parameter's maxpin so that the following condition is satisfied:
(machine's memory size) x (maxpin setting)/100 a + b^# + c
a: Size of shared memory segment for the unit controller
b: Sum of the sizes of all shared memory segments for global buffers
c: Sum of the sizes of all shared memory segments used by the OS that fixes shared memory or the additional program products
#: Add this value when fixed is specified in the pd_dbbuff_attribute operand.
You can use an AIX command to determine whether or not shared memory has been fixed in memory; for details, see the AIX 5L manual.

88) pd_dbbuff_attribute = free | fixed

Specifies whether to fix the shared memory used by the global buffer in the real memory. Note that the AIX 5L version of HiRDB(32-bit mode) or the Linux version of HiRDB does not support fixing of the shared memory, and therefore specification of fixed for this operand is invalid.

free (default value for 64-bit mode):: Do not fix the shared memory to be used by the global buffer in the real memory.

fixed (default value for 32-bit mode):: Fix the shared memory to be used by the global buffer in the real memory.

Advantage: Fixing the shared memory to be used by the global buffer in the real memory ("fixed" specified) prevents shared memory paging, thus improving the performance of accesses to the shared memory.

Specification guidelines

Whether or not the shared memory is to be fixed should be determined based on the computed shared memory size and the real memory size of the server machine. If a memory page that is quite large relative to the real memory is fixed, the result may be frequent paging or a virtual memory shortage. Therefore, how much real memory there is and the amount of memory to be occupied by the shared memory pool need to be evaluated carefully. For the formula for computing the shared memory size to be used by the global buffer, see the HiRDB Version 8 Installation and Design Guide.
When the size of the shared memory to be page-fixed is subtracted from the size of the real memory, the result should not equal or exceed half the size that is obtained by subtracting the size of the shared memory to be page-fixed from the swap area size.

Relationship to other facilities

If fixed is specified, the shared memory used by a dynamically modified global buffer is also fixed in the real memory. Therefore, carefully consider the real memory size before adding or modifying a global buffer.

Notes: If fixed is specified in the AIX 5L version, see the notes for the pd_shmpool_attribute operand.

Relationship to other operands

If v6compatible or v7compatible is specified in the pd_sysdef_default_option operand, the default value is as follows:

HiRDB in 32-bit mode: fixed
HiRDB in 64-bit mode: free

2.3.16 Operands related to shared memory