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Posted May 12, 2004

Oracle Background Processes - Page 3

By Amar Kumar Padhi

Lock processes

Process Name: LCK0 through LCK9

Max Processes: 10

Meant for Parallel server setups, the instance locks that are used to share resources between instances are held by the lock processes.

Block Server Process

Process Name: BSP0 through BSP9

Max processes: 10

Meant for Parallel server setups, Block server Processes have to do with providing a consistent read image of a buffer that is requested by a process of another instance, in certain circumstances.

Queue Monitor

Process Name: QMN0 through QMN9

Max Processes: 10

This is the advanced Queuing Time manager process. QMNn monitors the message queues. Failure of QMNn process will not cause the instance to fail.

Event Monitor

Process Name: EMN0/EMON

Max Processes: 1

This process is also related to Advanced Queuing, and is meant for allowing a publish/subscribe style of messaging between applications.


Process Name: RECO

Max processes: 1

Intended for distributed recovery. All in-doubt transactions are recovered by this process in the distributed database setup. RECO will connect to the remote database to resolve pending transactions.

Job Queue Processes

Process Name: J000 through J999 (Originally called SNPn processes)

Max Processes: 1000

Job queue processes carry out batch processing. All scheduled jobs are executed by these processes. The initialization parameter JOB_QUEUE_PROCESSES specifies the maximum job processes that can be run concurrently. If a job fails with some Oracle error, it is recorded in the alert file and a process trace file is generated. Failure of the Job queue process will not cause the instance to fail.


Process Name: Dnnn

Max Processes: -

Intended for Shared server setups (MTS). Dispatcher processes listen to and receive requests from connected sessions and places them in the request queue for further processing. Dispatcher processes also pickup outgoing responses from the result queue and transmit them back to the clients. Dnnn are mediators between the client processes and the shared server processes. The maximum number of Dispatcher process can be specified using the initialization parameter MAX_DISPATCHERS.

Shared Server Processes

Process Name: Snnn

Max Processes: -

Intended for Shared server setups (MTS). These processes pickup requests from the call request queue, process them and then return the results to a result queue. The number of shared server processes to be created at instance startup can be specified using the initialization parameter SHARED_SERVERS.

Parallel Execution Slaves

Process Name: Pnnn

Max Processes: -

These processes are used for parallel processing. It can be used for parallel execution of SQL statements or recovery. The Maximum number of parallel processes that can be invoked is specified by the initialization parameter PARALLEL_MAX_SERVERS.

Trace Writer

Process Name: TRWR

Max Processes: 1

Trace writer writes trace files from an Oracle internal tracing facility.

Input/Output Slaves

Process Name: Innn

Max Processes: -

These processes are used to simulate asynchronous I/O on platforms that do not support it. The initialization parameter DBWR_IO_SLAVES is set for this purpose.

Wakeup Monitor Process

Process Name: WMON

Max Processes: -

This process was available in older versions of Oracle to alarm other processes that are suspended while waiting for an event to occur. This process is obsolete and has been removed.


With every release of Oracle, new background processes have been added and some existing ones modified. These processes are the key to the proper working of the database. Any issues related to background processes should be monitored and analyzed from the trace files generated and the alert log.

» See All Articles by Columnist Amar Kumar Padhi

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