25.5.7 Definition of global buffers (standby-less system switchover (1:1) facility only)
(1) Global buffers for data (-r option global buffers)
The system configuration examples shown below are used to explain how to allocate global buffers for data when alternating units.
System configuration example 1
![[Figure]](figure/zu250501.gif)
pdbuffer -a gbuf01 -r RDAREA01,RDAREA02 -n 1000 -c
pdbuffer -a gbuf02 -r RDAREA03,RDAREA04 -n 1000 |
- Explanation
- This configuration does not use global buffers with the same names in the normal BES and the alternate BES.
- When the -c option is specified, gbuf01 will also be secured in the alternate BES. This global buffer is used when alternating units. However, this global buffer is not used during normal operation.
- When estimating shared memory that the global buffers for the alternate BES unit will use, be sure to add enough memory for gbuf01.
- The buffer hit rate will not decrease when alternating units.
System configuration example 2
![[Figure]](figure/zu250502.gif)
pdbuffer -a gbuf01 -r RDAREA01,RDAREA02,RDAREA03,RDAREA04 -n 1000 -c |
- Explanation
- This configuration uses global buffers with the same names in the normal BES and the alternate BES.
- With the -c option specified, gbuf01 of the alternate BES will be used when alternating units.
- The buffer hit rate may decrease when alternating units.
- The buffer size of gbuf01 in the alternate BES will be the maximum page length of the RDAREAs in the normal BES and alternate BES.
- When the -c option is omitted
- When the -c option is omitted, global buffers specified by the -o option are used when alternating units.
(2) Global buffers for index (-i option global buffer)
The system configuration examples shown below are used to explain how to allocate global buffers for index when alternating units.
System configuration example
![[Figure]](figure/zu250503.gif)
pdbuffer -a gbuf01 -i USER01.INDX01 -n 1000 -c |
- Explanation
- When the -c option is specified for a global buffer that uses row nonpartitioned index INDX01, gbuf01 will also be secured in the alternate BES. This global buffer is used when alternating units. However, this global buffer is not used during normal operation.
- When estimating shared memory that the global buffers for the alternate BES unit will use, be sure to add enough memory for gbuf01.
System configuration example
![[Figure]](figure/zu250504.gif)
pdbuffer -a gbuf02 -i USER01.INDX02 -n 1000 -c |
- Explanation
- When the -c option is specified for a global buffer that uses row partitioned index INDX02, gbuf02 will also be secured in the alternate BES. This global buffer is used when alternating units, so no access conflict with INDX02 occurs on BES2. However, this global buffer is not used during normal operation.
- When estimating shared memory that the global buffers for the alternate BES unit will use, be sure to have twice the size of gbuf02 available.
- When the -c option is omitted
- When the -c option is omitted, global buffers are used when alternating units according to the priorities explained below.
- Allocate a global buffer to the index RDAREA. If the -c option is specified for the global buffer, allocate the global buffer using the procedure explained in (1).
- The global buffer specified by the -o option is used.
(3) Global buffers for LOB (-b option global buffer)
The procedure for allocating global buffers for LOB when alternating units is the same as the procedure for allocating global buffers for data. However, if the -c option is omitted, data will be written to or read from the RDAREA directly without using a global buffer.
(4) -o option global buffers
An -o option global buffer in the alternate BES also uses the RDAREA in the normal BES when alternating units. The buffer size of the global buffer is the maximum page length of the RDAREA in the normal BES and alternate BES.
(5) Design guidelines for global buffers
Basically, specify the -c option for global buffers used by RDAREAs, indexes, and LOB RDAREAs in normal BES units.
- When the -c option is specified, the global buffer used when an alternating unit is created in the alternate BES. Therefore, be sure there is enough extra shared memory for use by the global buffer in the alternate BES unit. If there is not enough extra shared memory, do not specify the -c option.
- When using a global buffer for the alternate BES also in the RDAREA in the normal BES, the buffer size of this global buffer is the maximum page length of the RDAREA in the normal BES and alternate BES. Therefore, be sure to consider the page length of the RDAREAs when specifying the -c option.