Section 14.9. Summary


14.9. Summary

In this chapter you learned a number of topics relating to the DB2 process model. A connection is first accepted by a process called a listener, and there are different listeners for different communication protocols. After an application connects to a database, a process is created and assigned to do work on behalf of the application. This process is called a coordinator agent (db2agent). In a partitioned database environment, or if intra-partition parallelism is enabled, the coordinator agent distributes work to subagents (db2agntp). These subagents perform the work and return the result to the coordinator agent to return to the application.

Since DB2 processes live within the DB2 engine, processes are also called DB2 Engine Dispatchable Units (EDUs). A coordinator agent, a subagent, a page cleaner, and a listener agent are all examples of EDUs. EDUs are implemented as processes on Linux/UNIX platforms and as threads on Windows Platforms.

The DB2 system controller process (db2sysc) is the first process created when an instance starts. The db2sysc process will then spawn other critical instance-level processes, such as the db2gds (only on Linux/UNIX), db2resyn, db2pdbc, db2cart, and others. The db2gds is the Global Daemon Spawner processit spawns a lot of database-level processes.

There are four different types of DB agents: coordinator agents (db2agent), active subagents (db2agntp), associated idle subagents (db2agnta), and unassociated idle agents (db2agent (idle). Coordinator agents work on behalf of the application by communicating with other agents. Subagents are created in a DPF environment or when the INTRA_PARALLEL parameter is enabled. Associated subagents are nonactive agents (returned to the agent pool) that are still under the application coordinator agent's control. Unassociated idle agents are agents that are released by an application's coordinator agent (released to the agent pool) and thus can be used by any other application.

The number that the four types of agents can have are controlled by various Database Manager Configuration parameters, such as MAXAGENTS, MAX_COORDAGENTS, and NUM_ POOLAGENTS. Tuning these parameters properly helps increase database performance. You can use the database manager Snapshot Monitor to check the usage of these agents, and then you can tune them accordingly.

Connection concentrator is enabled when MAXCONNECTIONS is greater than MAX_ COORDAGENTS. When enabled, an application has to wait for a coordinator agent to become available to service it. Otherwise, it remains in an inactive state. This feature is useful when you want to limit the resources used by each connection, especially when you know these connections are often idle.



Understanding DB2(R. Learning Visually with Examples)
Understanding DB2: Learning Visually with Examples (2nd Edition)
ISBN: 0131580183
EAN: 2147483647
Year: 2004
Pages: 313

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