Database manager shared memory

Database manager shared memory is organized into several different memory areas. Configuration parameters enable you to control the sizes of these areas.

Figure 1 shows how database manager shared memory is allocated.

Figure 1. How memory is used by the database manager
Memory areas and the configuration parameters that control their sizes
Database Manager Shared Memory
Database Manager Shared Memory is affected by the following configuration parameters:
  • The audit_buf_sz configuration parameter determines the size of the buffer used in database auditing activities.
  • The mon_heap_sz configuration parameter determines the size of the memory area used for database system monitoring data.
  • For partitioned database systems, the Fast Communications Manager (FCM) requires substantial memory space, especially if the value of fcm_num_buffers is large. The FCM memory requirements are allocated from the FCM Buffer Pool.
Database global memory
Database global memory is affected by the size of the buffer pools and by the following database configuration parameters:
  • catalogcache_sz
  • database_memory
  • dbheap
  • locklist
  • pckcachesz
  • sheapthres_shr
  • util_heap_sz
Application global memory
Application global memory can be controlled by the appl_memory configuration parameter. The following database configuration parameters can be used to limit the amount of memory that any one application can consume:
  • applheapsz
  • stat_heap_sz
  • stmtheap
Agent private memory
Each agent requires its own private memory region. The data server creates as many agents as it needs and in accordance with configured memory resources. You can control the maximum number of coordinator agents using the max_coordagents database manager configuration parameter. The maximum size of each agent's private memory region is determined by the values of the following configuration parameters:
  • agent_stack_sz
  • sheapthres and sortheap
Agent/Application shared memory
The total number of agent/application shared memory segments for local clients is limited by the lesser of the following two values:
  • The total value of the maxappls database configuration parameter for all active databases
  • The value of the max_coordagents database configuration parameter
Note: In configurations where engine concentration is enabled (max_connections > max_coordagents), application memory consumption is limited by max_connections.
Agent/Application shared memory is also affected by the following database configuration parameters:
  • aslheapsz
  • rqrioblk