3.2.12 Operands related to shared memory

20) pd_shmpool_attribute = free | fixed
Specifies whether to fix the shared memory used by the HiRDB unit controller in memory. Note that the AIX edition of HiRDB (32-bit mode) does not support fixing of the shared memory, so specification of fixed in this operand will be ignored in this case.
free:
Do not fix the shared memory in memory. Depending on the size of the real memory, another page of shared memory might be created, adversely affecting performance.
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
Determine whether to fix shared memory 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 might 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 formulas used to calculate the shared memory sizes to be used by the unit controller and individual servers, see the HiRDB Version 9 Installation and Design Guide.
Operand default
When this operand is omitted, the specification of the same operand in the system common definition is assumed. When the same operand is also omitted in the system common definition, the default is free.
Relationship to other facilities
When fixed is specified in an AIX edition, the following constraints apply, which means that the inter-process memory communication facility cannot be used between a 64-bit-mode HiRDB server and a 32-bit-mode client process:
  • The operating system parameters of the OS must be set.
  • In the system common definition, the putenv EXTSHM ON environment variable cannot be set.
For details about the operating system parameters of the OS and the EXTSHM environment variable, see Estimating AIX 5L OS parameter values in the HiRDB Version 9 Installation and Design Guide
Notes
The following notes apply to specification of fixed in AIX:
  • Set operating system parameters for the OS. If the applicable operating system parameters for the OS are not set, this operand will be ignored. For details about the operating system parameters to set for the OS, see Estimating AIX 5L OS parameter values in the HiRDB Version 9 Installation and Design Guide.
  • You can use an AIX command to determine whether shared memory has been fixed in memory. For details, see the applicable AIX manual.
21) pd_dbbuff_attribute = free | fixed
Specifies whether to fix the shared memory used by the global buffers in the real memory. Note that the AIX edition of HiRDB (32-bit mode) does not support fixing of the shared memory, so specification of fixed in this operand will be ignored in this case.
free:
Do not fix the shared memory to be used by the global buffer in the real memory.
fixed:
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
  • To emphasize performance when there is ample real memory, specify fixed.
  • Determine whether to fix shared memory 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 might 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 formulas used to calculate the shared memory size to be used by the global buffer, see the HiRDB Version 9 Installation and Design Guide.
  • When the size of the shared memory to be page-fixed is subtracted from the size of the real memory, as a guideline, make sure that the result does 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.
Operand default
When this operand is omitted, the specification of the same operand in the system common definition is assumed. When the same operand is also omitted in the system common definition, the default is free.
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.
  • When fixed is specified in an AIX edition, the following constraints apply, which means that the inter-process memory communication facility cannot be used between a 64-bit-mode HiRDB server and a 32-bit-mode client process:
    [Figure]The operating system parameters of the OS must be set.
    [Figure]In the system common definition, the putenv EXTSHM ON environment variable cannot be set.
    For details about the operating system parameters of the OS and the EXTSHM environment variable, see Estimating AIX 5L OS parameter values in the HiRDB Version 9 Installation and Design Guide.
Notes
The following notes apply to specification of fixed in an AIX edition:
  • Set operating system parameters for the OS. If the applicable operating system parameters for the OS are not set, this operand will be ignored. For details about the operating system parameters to set for the OS, see Estimating AIX 5L OS parameter values in the HiRDB Version 9 Installation and Design Guide.
  • You can use an AIX command to determine whether shared memory has been fixed in memory. For details, see the applicable AIX manual.