organizes memory and the many configuration parameters that affect memory usage is essential.
Instance shared memory (also known as database-manager shared memory) is allocated when the database is started. All other memory is attached or allocated from the instance shared memory. When the first application connects or attaches to a database, database shared, application shared, and agent private memory areas are allocated. Instance shared memory can be controlled by the INSTANCE_MEMORY configuration parameter of the database manager. By default, this parameter is set to automatic so that DB2 calculates the amount of memory allocated for the instance.
Database shared memory (also known as Database Global memory) is allocated when a database is activated or connected to for the first time. This memory is used across all applications that might connect to the database. Database shared memory can be controlled by the DATABASE_MEMORY configuration parameter at database level. By default, this parameter is set to automatic so that DB2 calculates the amount of memory allocated for the database. The following memory areas contained in the database shared memory are extremely important in performance tuning:
Buffer pools Lock list Database heap (includes the log buffer) Utility heap Package cache Catalog cache
Although the total amount of database global memory cannot be increased or decreased while the database is active, all of the memory areas listed above can be changed dynamically while the database is running. Refer to Chapter 8, “Tuning DB2 for Content Manager� on page 171 for an in-depth look at the configuration parameter values and recommendations. A system administrator needs to consider overall balance of memory usage on the system. Different applications running on the operating system might use memory in different ways. For the Content Manager application, the majority of system memory should not be given to DB2 when using AIX. Only about 20% of available memory should be assigned to DB2 and the rest should be used for disk cache. As you will see often in this book, tuning is mandatory and should be performed on a regular basis to maintain optimal system performance.
Chapter 2. Content Manager base products
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