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Administration

New Background Processes in Oracle Database 11g

Oracle Database 11g introduced 56 new background processes.

Note:
The following post based on the Oracle Database 11g and briefly describes some important processes.

These processes are mandatory and can be found in all typical database environment.

    • PMON – Process Monitor
    • Recover failed user process, Releasing resource, Rollback uncommitted Transaction

    • SMON – System Monitor
    • Instance recovery, Cleans and releases temporary segments

    • LGWR – Log Writer (Redo etc.)
    • Writes redo entries from redo log buffer to disk (Redo log file)

    • CKPT – Checkpoint
    • Ensures data consistency and easy database recovery in case of crash by sychronizing all the data file headers and control files with recent checkpoint information.

    • DBW0…j – DB Writer
    • Flushing or writing modified dirty data (buffers) from database buffer cache to disks (datafiles). You can configure addition DB writer processes (up to 20) from DBW0-DBW9 and DBWa through DBWj.

    • RECO – Distributed Recovery
    • Recoverer is responsible for recovering failed distributed transactions in a distributed database.

    • MMON & MMNL – Manageability Monitor and Manageability Monitor Lite
    • MMON performs tasks related to AWR such as taking snapshots, capturing statistics value for recently modified SQL objects and writes when a metric violates its threshold value.
      MMNL writes statistics from the Active Session History (ASH) buffer in the SGA to disk. MMNL writes to disk when the ASH buffer is full.

    • DIAG – Diagnostic Capture
    • Prior to Oracle database 11g, DIAG was used in RAC environmnent. Monitors overall health of the instance and performs diagnostic dumps requested by other processes and dumps triggered by process or instance termination.

Followings are optional and used by specific database feature.

    • ARCn – Archiver Process
    • Responsible for copying online redo log to archival storage before being reused. Runs only when database is in Archivelog Mode.

    • CJQ0 – Job Queue Coordinator Process
    • Job Queue coordinator is responsible for managing scheduled job processes within the database.

    • Dnnn – Dispatcher Process
    • Performs network communication in the shared server architecture

    • MMAN – Memory Manager
    • Responsible for managing instance memory based on the workloads.

    • PSP0 – Process Spawner Process
    • Spawns Oracle background processes whenever needed.

    • QMNC – AQ (Advanced Queuing) Coordinator Process
    • Facilitating various background activities required by AQ and Oracle Streams.

These are introduced in Oracle Database 11g. The first three is mandatory and others could be running depending upon the features being used.

    • DIA0 – Diagnostic
    • Responsible for detecting hangs and resolving deadlocks

    • GEN0 – General Task Execution Process
    • performs required tasks including SQL and DML

    • VKTM – Virtual Keeper of TiMe Process
    • Responsible for providing a wall-clock time (updated every second) and reference-time counter (updated every 20 ms) and available only when running at elevated priority.

    • DBRM – DataBase Resource Manager
    • Performs resource manager tasks setting resource plans.

    • FBDA – Flashback Data Archiver Process
    • Archives historical rows for tracked tables into flashback data archives and manages archive space, organization, and retention

    • SMCO – Space Management Coordinator
    • Coordinates the execution of various space management tasks

    • Wnnn – Space Management Slaves
    • Performs various background space management tasks, including proactive space allocation and space reclamation

    • RCBG – Result Cache BackGround
    • Handles result cache messages.

    • VKRM – Virtual Scheduler for Resource Manager Process
    • Schedules Resource Manager Activity. Serves as centralized scheduler for Resource Manager activity. VKRM manages the CPU scheduling for all managed Oracle processes.

More description about all these processes can be found in Oracle Database Reference 11g Reference – Appendix F

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