How much memory to configure

Memory is the most important consideration when you are configuring Adaptive Server. Memory is consumed by various configuration parameters, thread pools, procedure caches, and data caches. Correctly setting the values of the configuration parameters and the caches is critical to good system performance.

The total memory allocated during start up is the sum of the memory required for all Adaptive Server configuration requirements. This value is accumulated by Adaptive Server from the read-only configuration parameter total logical memory. The configuration parameter max memory must be greater than or equal to total logical memory. max memory indicates the amount of memory you allow for Adaptive Server needs.

Adaptive Server allocates memory based on the value of total logical memory at start up. However, if you have set the configuration parameter allocate max shared memory, the amount of memory Adaptive Server allocates is based on the value of max memory. This allows a system administrator to tell Adaptive Server to allocate, at start up, the maximum allowed, which may be considerably more than the value of total logical memory at that time.

The key points for memory configuration are:

What remains after all other memory needs have been met is available for the procedure cache and the data cache. Figure 5-1 shows how memory is divided.

Figure 5-1: How Adaptive Server uses memory

Image shows a stack consisting of physical memory and total logical memory. Physical memory consists of total physical memroy, data cache, data cache overhead, procedure cache, kernel and server structures, static overhead, Adaptive Server executable, and the OS. Total logical memory is made of all this except the OS.