Adjusting the Amount of Memory

Use the following formula as a starting point for estimating the amount of shared memory to allocate to decision-support queries:

DS_TOTAL_MEMORY = p_mem - os_mem - rsdnt_mem - 
                  (128 kilobytes * users) - other_mem 

p_mem

represents the total physical memory that is available on the host computer.

os_mem

represents the size of the operating system, including the buffer cache.

resdnt_mem

represents the size of Informix resident shared memory.

users

is the number of expected users (connections) specified in the NETTYPE configuration parameter.

other_mem

is the size of memory used for other (non-IBM Informix) applications.

The value for DS_TOTAL_MEMORY that is derived from this formula serves only as a starting point. To arrive at a value that makes sense for your configuration, you must monitor paging and swapping. (Use the tools provided with your operating system to monitor paging and swapping.) When paging increases, decrease the value of DS_TOTAL_MEMORY so that processing the OLTP workload can proceed.

The amount of memory that is granted to a single parallel database query depends on many system factors, but in general, the amount of memory granted to a single parallel database query is proportional to the following formula:

memory_grant_basis = (DS_TOTAL_MEMORY/DS_MAX_QUERIES) *
               (PDQPRIORITY / 100) *
               (MAX_PDQPRIORITY / 100)