Spotlight on DB2 6.9.3 - User Guide

Memory Pool types

The database manager controls all shared memory usage on the system through the following top down hierarchy:

• Database manager global shared memory. Also known as instance shared memory, this is the primary memory allocation that the database manager uses when assigning memory for databases and applications. It is allocated when DB2 starts and is not deallocated until DB2 is stopped.
• Database global shared memory. Database global memory is allocated by the database manager whenever a database is activated or connected to for the first time, and it is used for all applications that connect to the database. The size of this space is controlled by the database_memory parameter.

• Application global shared memory. This memory is allocated to applications under the following conditions:

  • In a partitioned environment
  • In a non-partitioned environment with intra-partition parallelism turned on
  • In an environment that has a connection concentrator enabled, you can assign several applications to an application group for the purpose of sharing memory. The database manager assigns each application group its own allocation of shared memory. This sharing improves system performance by reducing the possibility of unnecessarily over-allocating memory.

  The size of Application global shared memory is controlled by the Application Control Heap Size (APP_CTL_HEAP_SZ) parameter.

• Agent Private Memory. Agent private memory is allocated when a connect request or a new SQL request is made in a parallel environment. It contains memory allocations used for this specific agent only. Examples of agent private memory are the sort heap and the application heap.
• Agent/Application Shared Memory. This memory is used for SQL request and response communications between an agent and its client application.

Memory Pool tabs

The Spotlight drilldowns that contain tabs for memory pools are as follows:

• Database Manager Summary
• Databases
• Client Applications

The following table lists the different memory allocations, the DB2 parameter used to control and adjust their sizes, and the most likely drilldown where information about a particular heap can be found. It is important to keep in mind that information for any of the heaps can be displayed in any of drilldowns listed. What this chart does is list the drilldown that most commonly displays the statistics for a particular memory segment.

1 Nearly all buffer pool memory is sized automatically by the Database Manager and is allocated out of database shared memory. This reduces the need for increasing dbheap when buffer pools grow larger.

2 FCM memory requirements are either allocated from the FCM Buffer Pool, or from both the Database Manager Shared Memory and the FCM Buffer Pool, depending on whether or not the partitioned database system uses multiple logical partitions.