DB2 Memory Architecture

                DB2 is very interesting database product which can grow in size as much you want,

 literally from couple MBs to Multi-Terabytes. Capacity totally depends on a) Disk where the

real data will be stored, b) Memory allocation which is utilized to process the multi-terabytes

 of data to end users.

Lets talk how DB2 manages memory : DB2 memory is allocated in terms of shared memory

 and private memory. Shared memory is the one which is being shared by all of the db2 agents

 and gets allocated as soon as Instance/database is started. Whereas private memory is the

one which is used by db agents individually.

Let's understand first about the shared memory : This is allocated at 3 different levels :
1. Instance
2. Database
3. Application

Instace level shared memory is allocated when its started, and its de-allocated as soon

 as you stop it. Its been controlled through following Instance configuration parameters :

MON_HEAP_SZ
AUDIT_BUF_SZ
FCM_NUM_BUFFERS

Database level shared memory is allocated when its either activated explicitly or with the

 first db connection, and de-allocated when its either deactivated explicitly or with the reset

of last db connection.

BUFFERPOOL
PACKAGE CACHE
CATALOG CACHE
LOCKLIST
DATABASE HEAP
UTILITY HEAP
SHARED SORT HEAP (if INTRA_PARALLEL is enabled)

Application level shared memory is not allocated in every situation. It gets allocated when the

 database agents need to coordinate with each other. This happens in a specific scenario when

you have either multi-partitioned database or have enabled the intra_parallel configuration in a

single partitioned database. In these specific scenario, a single db agent forks the multiple

 subagents to serve the request in parallel but still share the same application memory which

 was allocated to their parent agent.

APP_GROUP_MEM_SZ
GROUPHEAP_RATIO
APP_CTL_HEAP_SZ

Private memory Its allocated through a database connection when its assigned to a database

 agent. Its usage is very dynamic and totally depends on how long that specific agent is busy

in processing the request. This memory is utilized to perform sort,to acquire lock,to build the

 access plan of SQL etc.

APPLICATION HEAP
SORTHEAP
STATEMENT HEAP
STATISTICS HEAP
QUERY HEAP
JAVA INTERPRETER HEAP

                You can monitor the usage of these memory allocation using db2mtrk or DB2PD

 utility and you can keep re-adjusting based on the database size growth and its utilization.