After you create a data cache, you can divide it into memory pools, each with a different I/O size. In any cache, you can have only one pool of each I/O size. The minimum size you can create a memory pool is the size of the server’s logical page. Memory pools larger than this must be a power of two and can be a maximum size of one extent.
When Adaptive Server performs large I/Os, multiple pages are read into the cache at the same time. These pages are always treated as a unit; they age in the cache and are written to disk as a unit.
By default, when you create a named data cache, all of its space is assigned to the default memory pool. Creating additional pools reassigns some of that space to other pools, reducing the size of the default memory pool. For example, if you create a data cache with 50MB of space, all the space is assigned to the 2K pool. If you configure a 4K pool with 30MB of space in this cache, the 2K pool is reduced to 20MB.
Figure 19-2: Configuring a cache and a 4K memory pool
After you create the pools, you can move space between them. For example, in a cache with a 20MB 2K pool and a 30MB 4K pool, you can configure a 16K pool, taking 10MB of space from the 4K pool.
Figure 19-3: Moving space from an existing pool to a new pool
The commands that move space between pools within a cache do not require a restart of Adaptive Server, so you can reconfigure pools to meet changing application loads with little impact on server activity.
In addition to creating pools in the caches you configure, you can add memory pools for I/Os up to 16K to the default data cache.
The syntax for configuring memory pools is:
sp_poolconfig cache_name, "memsize[P|K|M|G]", "config_poolK" [, "affected_poolK"]
Pool configuration sets the config_pool to the size specified in the command. It always affects a second pool (the affected_pool) by moving space to or from that pool. If you do not specify the affected_pool, the space is taken from or allocated to the 2K pool. The minimum size for a pool is 512K.
This example creates a 7MB pool of 16K pages in the pubs_cache data cache:
sp_poolconfig pubs_cache, "7M", "16K"
This command reduces the size of the memory pool. To see the current configuration, run sp_cacheconfig, giving only the cache name:
sp_cacheconfig pubs_cache
Cache Name Status Type Config Value Run Value ------------------------ --------- -------- ------------ ------------ pubs_cache Active Mixed 10.00 Mb 10.00 Mb ------------ ------------ Total 10.00 Mb 10.00 Mb ======================================================================= Cache: pubs_cache, Status: Active, Type: Mixed Config Size: 10.00 Mb, Run Size: 10.00 Mb Config Replacement: strict LRU, Run Replacement: strict LRU Config Partition: 1, Run Partition: 1 IO Size Wash Size Config Size Run Size APF Percent -------- --------- ------------ ------------ ----------- 2 Kb 2048 Kb 0.00 Mb 3.00 Mb 10 16 Kb 1424 Kb 7.00 Mb 7.00 Mb 10
You can also create memory pools in the default data cache.
In the following example, you start with this cache configuration:
Cache Name Status Type Config Value Run Value ------------------------ --------- -------- ------------ ------------ default data cache Active Default 25.00 Mb 42.29 Mb ------------ ------------ Total 25.00 Mb 42.29 Mb ======================================================================= Cache: default data cache, Status: Active, Type: Default Config Size: 25.00 Mb, Run Size: 42.29 Mb Config Replacement: strict LRU, Run Replacement: strict LRU Config Partition: 1, Run Partition: 1 IO Size Wash Size Config Size Run Size APF Percent -------- --------- ------------ ------------ ----------- 2 Kb 8662 Kb 0.00 Mb 42.29 Mb 10
This command creates a 16K pool in the default data cache that is 8 megabytes:
sp_poolconfig "default data cache", "8M", "16K"
It results in this configuration, reducing the “Run Size” of the 2K pool:
Cache Name Status Type Config Value Run Value ------------------------ --------- -------- ------------ ------------ default data cache Active Default 25.00 Mb 42.29 Mb ------------ ------------ Total 25.00 Mb 42.29 Mb ======================================================================= Cache: default data cache, Status: Active, Type: Default Config Size: 25.00 Mb, Run Size: 42.29 Mb Config Replacement: strict LRU, Run Replacement: strict LRU Config Partition: 1, Run Partition: 1 IO Size Wash Size Config Size Run Size APF Percent -------- --------- ------------ ------------ ----------- 2 Kb 8662 Kb 0.00 Mb 34.29 Mb 10 16 Kb 1632 Kb 8.00 Mb 8.00 Mb 10
You do not need to configure the size of the 2K memory pool in caches that you create. Its “Run Size” represents all the memory not explicitly configured to other pools in the cache.
