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Oracle® Database Reference
12c Release 1 (12.1)

E17615-23
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F Background Processes

Table F-1 describes Oracle Database background processes. In this context, a background process is defined as any process that is listed in V$PROCESS and has a non-null value in the PNAME column.

The External Properties column lists the type of instance in which the process runs. If the process is specific to a particular feature, then the column names the feature.

Note:

When the THREADED_EXECUTION initialization parameter is set to TRUE on Linux and UNIX, the DBW, PMON, PSP, and VKTM background processes run as operating system processes, and the other background processes run as operating system threads.

See "THREADED_EXECUTION" for more information about the THREADED_EXECUTION initialization parameter.

Table F-1 Background Processes

Name Expanded Name Short Description Long Description External Properties

ABMR

Auto BMR Background Process

Coordinates execution of tasks such as filtering duplicate block media recovery requests and performing flood control

When a process submits a block media recovery request to ABMR, it dynamically spawns slave processes (BMRn) to perform the recovery. ABMR and BMRn terminate after being idle for a long time.

See Also: Oracle Database Backup and Recovery User's Guide

Database instances

ACFS

ASM Cluster File System CSS Process

Tracks the cluster membership in CSS and informs the file system driver of membership changes

ACFS delivers CSS membership changes to the Oracle cluster file system. These membership changes are required for the file system to maintain file system consistency within the cluster.

Oracle ASM instances, Oracle RAC

ACMS

Atomic Control File to Memory Service Process

Coordinates consistent updates to a control file resource with its SGA counterpart on all instances in an Oracle RAC environment

The ACMS process works with a coordinating caller to ensure that an operation is executed on every instance in Oracle RAC despite failures. ACMS is the process in which a distributed operation is called. As a result, this process can exhibit a variety of behaviors. In general, ACMS is limited to small, nonblocking state changes for a limited set of cross-instance operations.

Database instances, Oracle RAC

APnn

Database Apply Process Coordinator Process

Obtains transactions from the reader server and passes them to apply servers

The coordinator process name is APnn, where nn can include letters and numbers.

For more information about the coordinator process, see V$STREAMS_APPLY_COORDINATOR for Oracle Streams, V$XSTREAM_APPLY_COORDINATOR for XStream, and V$GG_APPLY_COORDINATOR for Oracle GoldenGate.

See Also: Oracle Streams Concepts and Administration and Oracle Database XStream Guide

Database instances, Logical Standby, Streams Apply, XStream Inbound servers, XStream Outbound servers, GoldenGate Integrated Replicat

AQPC

AQ Process Coordinator

Per instance AQ global coordinator

AQPC is responsible for performing administrative tasks for AQ Master Class Processes including commands like starting, stopping, and other administrative tasks. This process is automatically started on instance startup.

Database instances Advanced Queueing

ARBn

ASM Rebalance Process

Rebalances data extents within an ASM disk group

Possible processes are ARB0-ARB9 and ARBA.

Oracle ASM instances

ARCn

Archiver Process

Copies the redo log files to archival storage when they are full or an online redo log switch occurs

ARCn processes exist only when the database is in ARCHIVELOG mode and automatic archiving is enabled, in which case ARCn automatically archives online redo log files. LGWR cannot reuse and overwrite an online redo log group until it has been archived.

The database starts multiple archiver processes as needed to ensure that the archiving of filled online redo logs does not fall behind. Possible processes include ARC0-ARC9 and ARCa-ARCt.

The LOG_ARCHIVE_MAX_PROCESSES initialization parameter specifies the number of ARCn processes that the database initially invokes.

See Also: Oracle Database Concepts and Oracle Database Administrator's Guide

Database instances

ARSn

ASM Recovery Slave Process

Recovers ASM transactional operations

The ASM RBAL background process coordinates and spawns one or more of these slave processes to recover aborted ASM transactional operations. These processes run only in the Oracle ASM instance.

Possible processes are ARS0-ARS9.

Oracle ASM instances

ASMB

ASM Background Process

Communicates with the ASM instance, managing storage and providing statistics

ASMB runs in Oracle ASM instances when the ASMCMD cp command runs or when the database instance first starts if the server parameter file is stored in Oracle ASM. ASMB also runs with Oracle Cluster Registry on Oracle ASM.

Database instances, Oracle ASM instances

ASnn

Database Apply Reader or Apply Server

  • Computes dependencies between logical change records (LCRs) and assembles messages into transactions (Reader Server)

  • Applies LCRs to database objects or passes LCRs and user messages to their appropriate apply handlers (Apply Server)

When the reader server finishes computing dependencies between LCRs and assembling transactions, it returns the assembled transactions to the coordinator process. Query V$STREAMS_APPLY_READER, V$XSTREAM_APPLY_READER, and V$GG_APPLY_READER for information about the reader server background process.

An apply server receives the transactions from the coordinator background process, and either applies database changes in LCRs or sends LCRs or messages to apply handlers. Apply servers can also enqueue a queue. If an apply server encounters an error, then it then tries to resolve the error with a user-specified conflict handler or error handler. If an apply server cannot resolve an error, then it rolls back the transaction and places the entire transaction, including all of its messages, in the error queue. When an apply server commits a completed transaction, this transaction has been applied. When an apply server places a transaction in the error queue and commits, this transaction also has been applied. Query V$STREAMS_APPLY_SERVER for information about the apply server background process. For XStream Inbound servers, query V$XSTREAM_APPLY_SERVER. For GoldenGate Integrated Replicat, query V$GG_APPLY_SERVER.

The coordinator process name is ASnn, where nn can include letters and numbers.

Database instances, XStream Outbound servers, XStream Inbound servers, GoldenGate Integrated Replicat

BMRn

Automatic Block Media Recovery Slave Pool Process

Fetches blocks from a real-time readable standby database

When a process submits a block media recovery request to ABMR, it dynamically spawns slave processes (BMRn) to perform the recovery. BMRn processes fetch blocks from a real-time readable standby database. ABMR and BMRn terminate after being idle for a long time.

See Also: Oracle Database Backup and Recovery User's Guide

Database instances

Bnnn

ASM Blocking Slave Process for GMON

Performs maintenance actions on Oracle ASM disk groups

Bnnn performs actions that require waiting for resources on behalf of GMON. GMON must be highly available and cannot wait.

A Bnnn slave is spawned when a disk is taken offline in an Oracle ASM disk group. Offline timer processing and drop of the disk are performed in this slave. Up to five process (B000 to B004) can exist depending on the load.

Oracle ASM instances

BWnn

Database Writer Process

Writes modified blocks from the database buffer cache to the data files

See the Long Description for the DBWn process in this table for more information about the BWnn process.

Database instances

CJQ0

Job Queue Coordinator Process

Selects jobs that need to be run from the data dictionary and spawns job queue slave processes (Jnnn) to run the jobs

CJQ0 is automatically started and stopped as needed by Oracle Scheduler.

The JOB_QUEUE_PROCESSES initialization parameter specifies the maximum number of processes that can be created for the execution of jobs. CJQ0 starts only as many job queue processes as required by the number of jobs to run and available resources.

See Also: Oracle Database Concepts and Oracle Database Administrator's Guide

Database instances

CKPT

Checkpoint Process

Signals DBWn at checkpoints and updates all the data files and control files of the database to indicate the most recent checkpoint

At specific times CKPT starts a checkpoint request by messaging DBWn to begin writing dirty buffers. On completion of individual checkpoint requests, CKPT updates data file headers and control files to record most recent checkpoint.

CKPT checks every three seconds to see whether the amount of memory exceeds the value of the PGA_AGGREGATE_LIMIT initialization parameter, and if so, takes the action described in "PGA_AGGREGATE_LIMIT".

See Also: Oracle Database Concepts

Database instances, Oracle ASM instances

CPnn

Database Capture Process

Captures database changes from the redo log by using the infrastructure of LogMiner

The capture process name is CPnn, where nn can include letters and numbers. The underlying LogMiner process name is MSnn, where nn can include letters and numbers. The capture process includes one reader server that reads the redo log and divides it into regions, one or more preparer servers that scan the redo log, and one builder server that merges redo records from the preparer servers. Each reader server, preparer server, and builder server is a process. Query the V$STREAMS_CAPTURE, V$XSTREAM_CAPTURE, and V$GOLDENGATE_CAPTURE view for information about this background process.

See Also: Oracle Streams Concepts and Administration and Oracle Database XStream Guide

Database instances, XStream Outbound Servers, Oracle Streams

CSnn

I/O Calibration Process

Issues I/Os to storage as part of storage calibration.

CSnn slave processes are started on execution of the DBMS_RESOURCE_MANAGER.CALIBRATE_IO() procedure. There is one slave process per CPU on each node of the database.

Database instances, Oracle RAC

CTWR

Change Tracking Writer Process

Tracks changed data blocks as part of the Recovery Manager block change tracking feature

CTWR tracks changed blocks as redo is generated at a primary database and as redo is applied at a standby database. The process is slightly different depending on the type of database.

See Also: Oracle Database Backup and Recovery User's Guide

Database instances

CXnn

Streams Propagation Sender Process

Sends LCRs to a propagation receiver

The propagation sender process name is CXnn, where nn can include letters and numbers. In an Oracle Streams combined capture and apply optimization, the propagation sender sends LCRs directly to the propagation receiver to improve performance. The propagation receiver passes the LCRs to an apply process. Query V$PROPAGATION_SENDER for information about a propagation sender.

Database instances, XStream Outbound Server, Oracle Streams

DBRM

Database Resource Manager Process

Sets resource plans and performs other tasks related to the Database Resource Manager

If a resource plan is not enabled, then this process is idle.

See Also: Oracle Database Administrator's Guide

Database instances

DBWn

Database Writer Process

Writes modified blocks from the database buffer cache to the data files

The primary responsibility of the Database Writer Process is to write data blocks to disk. It also handles checkpoints, file open synchronization, and logging of Block Written records.

In many cases the blocks that the Database Writer Process writes are scattered throughout the disk. Thus, the writes tend to be slower than the sequential writes performed by LGWR. The Database Writer Process performs multiblock writes when possible to improve efficiency. The number of blocks written in a multiblock write varies by operating system.

The DB_WRITER_PROCESSES initialization parameter specifies the number of Database Writer Processes. There can be 1 to 100 Database Writer Processes. The names of the first 36 Database Writer Processes are DBW0-DBW9 and DBWa-DBWz. The names of the 37th through 100th Database Writer Processes are BW36-BW99. The database selects an appropriate default setting for the DB_WRITER_PROCESSES parameter or adjusts a user-specified setting based on the number of CPUs and processor groups.

See Also: "DB_WRITER_PROCESSES"

Database instances

DIA0

Diagnostic Process


Detects and resolves hangs and deadlocks
 

Database instances, Oracle ASM instances

DIAG

Diagnostic Capture Process


Performs diagnostic dumps

DIAG performs diagnostic dumps requested by other processes and dumps triggered by process or instance termination. In Oracle RAC, DIAG performs global diagnostic dumps requested by remote instances.

Database instances, Oracle ASM instances

DMnn

Data Pump Master Process

Coordinates the Data Pump job tasks performed by Data Pump worker processes and handles client interactions

The Data Pump master (control) process is started during job creation and coordinates all tasks performed by the Data Pump job. It handles all client interactions and communication, establishes all job contexts, and coordinates all worker process activities on behalf of the job.

Database instances, Data Pump

DMON

Data Guard Broker Monitor Process

Manages and monitors a database that is part of a Data Guard broker configuration

When you start the Data Guard broker, a DMON process is created. DMON runs for every database instance that is managed by the broker. DMON interacts with the local database and the DMON processes of the other databases to perform the requested function. DMON also monitors the health of the broker configuration and ensures that every database has a consistent description of the configuration.

DMON maintains profiles about all database objects in the broker configuration in a binary configuration file. A copy of this file is maintained by the DMON process for each of the databases that belong to the broker configuration. The process is created when the DG_BROKER_START initialization parameter is set to true.

See Also: Oracle Data Guard Broker

Database instances, Data Guard

Dnnn

Dispatcher Process

Performs network communication in the shared server architecture

In the shared server architecture, clients connect to a dispatcher process, which creates a virtual circuit for each connection. When the client sends data to the server, the dispatcher receives the data into the virtual circuit and places the active circuit on the common queue to be picked up by an idle shared server. The shared server then reads the data from the virtual circuit and performs the database work necessary to complete the request. When the shared server must send data to the client, the server writes the data back into the virtual circuit and the dispatcher sends the data to the client. After the shared server completes the client request, the server releases the virtual circuit back to the dispatcher and is free to handle other clients.

Several initialization parameters relate to shared servers. The principal parameters are: DISPATCHERS, SHARED_SERVERS, MAX_SHARED_SERVERS, LOCAL_LISTENER, REMOTE_LISTENER.

See Also: Oracle Database Concepts

Database instances, shared servers

DSKM

Slave Diskmon Process

Acts as the conduit between the database, Oracle ASM instances, and the Master Diskmon daemon to communicate information to Exadata storage

This process is active only if Exadata Storage is used. DSKM performs operations related to Exadata I/O fencing and Exadata cell failure handling.

Oracle ASM instances, Exadata

DWnn

Data Pump Worker Process

Performs Data Pump tasks as assigned by the Data Pump master process

The Data Pump worker process is responsible for performing tasks that are assigned by the Data Pump master process, such as the loading and unloading of metadata and data.

Database instances

EMNC

EMON Coordinator Process

Coordinates database event management and notifications

EMNC is a master background process that coordinates event management and notification activity in the database, including Streams Event Notifications, Continuous Query Notifications, and Fast Application Notifications.

Database instances

Ennn

EMON Slave Process

Performs database event management and notifications

The database event management and notification load is distributed among the EMON slave processes. These processes work on the system notifications in parallel, offering a capability to process a larger volume of notifications, a faster response time, and a lower shared memory use for staging notifications.

Database instances

FBDA

Flashback Data Archiver Process

Archives historical rows for tracked tables into flashback data archives and manages archive space, organization, and retention

When a transaction that modifies a tracked table commits, FBDA stores the pre-image of the rows in the archive. FDBA maintains metadata on the current rows and tracks how much data has been archived.

FBDA is also responsible for automatically managing the flashback data archive for space, organization (partitioning tablespaces), and retention. FBDA also keeps track of how far the archiving of tracked transactions has progressed.

See Also: Oracle Database Development Guide

Database instances

FENC

Fence Monitor Process

Processes fence requests for RDBMS instances which are using Oracle ASM instances

CSS monitors RDBMS instances which are connected to the Oracle ASM instance and constantly doing I/Os. When the RDBMS instance terminates due to a failure, all the outstanding I/O's from the RDBMS instance should be drained and any new I/O's rejected. FENC receives and processes the fence request from CSSD.

Oracle ASM instances

FMON

File Mapping Monitor Process

Manages mapping information for the Oracle Database file mapping interface

The DBMS_STORAGE_MAP package enables you to control the mapping operations. When instructed by the user, FMON builds mapping information and stores it in the SGA, refreshes the information when a change occurs, saves the information to the data dictionary, and restores it to the SGA at instance startup.

FMON is started by the database whenever the FILE_MAPPING initialization parameter is set to true.

Database instances, Oracle ASM instances

FSFP

Data Guard Broker Fast Start Failover Pinger Process

Maintains fast-start failover state between the primary and target standby databases

FSFP is created when fast-start failover is enabled.

Database instances, Data Guard

GCRn

Global Conflict Resolution Slave Process

Performs synchronous tasks on behalf of LMHB

GCRn processes are transient slaves that are started and stopped as required by LMHB to perform synchronous or resource intensive tasks.

Database instances, Oracle ASM instances, Oracle RAC

GEN0

General Task Execution Process

Performs required tasks including SQL and DML

 

Database instances, Oracle ASM instances, Oracle ASM Proxy instances

GMON

ASM Disk Group Monitor Process

Monitors all mounted Oracle ASM disk groups

GMON monitors all the disk groups mounted in an Oracle ASM instance and is responsible for maintaining consistent disk membership and status information. Membership changes result from adding and dropping disks, whereas disk status changes result from taking disks offline or bringing them online.

Oracle ASM instances

GTXn

Global Transaction Process

Provides transparent support for XA global transactions in an Oracle RAC environment

These processes help maintain the global information about XA global transactions throughout the cluster. Also, the processes help perform two-phase commit for global transactions anywhere in the cluster so that an Oracle RAC database behaves as a single system to the externally coordinated distributed transactions.

The GLOBAL_TXN_PROCESSES initialization parameter specifies the number of GTXn processes, where n is 0-9 or a-j. The database automatically tunes the number of these processes based on the workload of XA global transactions. You can disable these processes by setting the parameter to 0. If you try to run XA global transactions with these processes disabled, an error is returned.

See Also: Oracle Real Application Clusters Administration and Deployment Guide

Database instances, Oracle RAC

Innn

Disk and Tape I/O Slave Process

Serves as an I/O slave process spawned on behalf of DBWR, LGWR, or an RMAN backup session

I/O slave process can be configured on platforms where asynchronous I/O support is not available. These slaves are started by setting the corresponding slave enable parameter in the server parameter file. The I/O slaves simulate the asynchronous I/O behavior when the underlying platform does not have native support for asynchronous I/O.

Database instances

INSV

Data Guard Broker Instance Slave Process

Performs Data Guard broker communication among instances in an Oracle RAC environment

INSV is created when the DG_BROKER_START initialization parameter is set to true.

Database instances, Data Guard

IPC0

IPC Service Background Process

Common background server for basic messaging and RDMA primitives based on IPC (Inter-process communication) methods.

IPC0 handles very high rates of incoming connect requests, as well as, completing reconfigurations to support basic messaging and RDMA primitives over several transports such as UDP, RDS, InfiniBand and RC.

Oracle RAC

Jnnn

Job Queue Slave Process

Executes jobs assigned by the job coordinator

Job slave processes are created or awakened by the job coordinator when it is time for a job to be executed.

Job slaves gather all the metadata required to run the job from the data dictionary. The slave processes start a database session as the owner of the job, execute triggers, and then execute the job. After the job is complete, the slave processes commit and then execute appropriate triggers and close the session. The slave can repeat this operation in case additional jobs need to be run.

Database instances

LCKn

Lock Process

Manages global enqueue requests and cross-instance broadcasts

The process handles all requests for resources other than data blocks. For examples, LCKn manages library and row cache requests. Possible processes are LCK0 and LCK1.

Database instances, Oracle ASM instances, Oracle RAC

LDDn

Global Enqueue Service Daemon Helper Slave

Helps the LMDn processes with various tasks

LDDn processes are slave processes spawned on demand by LMDn processes. They are spawned to help the dedicated LMDn processes with various tasks when certain workloads start creating performance bottlenecks. These slave processes are transient as they are started on demand and they can be shutdown when no longer needed. There can be up to 36 of these slave processes (LDD0-LDDz).

Database instances, Oracle ASM instances, Oracle RAC

LGnn

Log Writer Worker

Writes redo log

On multiprocessor systems, LGWR creates worker processes to improve the performance of writing to the redo log. LGWR workers are not used when there is a SYNC standby destination. Possible processes include LG00-LG99.

Database instances

LGWR

Log Writer Process

Writes redo entries to the online redo log

Redo log entries are generated in the redo log buffer of the system global area (SGA). LGWR writes the redo log entries sequentially into a redo log file. If the database has a multiplexed redo log, then LGWR writes the redo log entries to a group of redo log files.

See Also: Oracle Database Concepts and Oracle Database Administrator's Guide

Database instances, Oracle ASM instances

LMDn

Global Enqueue Service Daemon Process

Manages incoming remote resource requests from other instances

LMDn processes enqueue resources managed under Global Enqueue Service. In particular, they process incoming enqueue request messages and control access to global enqueues. They also perform distributed deadlock detections. There can be up to 36 of these processes (LMD0-LMDz).

Database instances, Oracle ASM instances, Oracle RAC

LMHB

Global Cache/Enqueue Service Heartbeat Monitor

Monitor the heartbeat of LMON, LMD, and LMSn processes

LMHB monitors LMON, LMD, and LMSn processes to ensure they are running normally without blocking or spinning.

Database instances, Oracle ASM instances, Oracle RAC

LMON

Global Enqueue Service Monitor Process

Monitors an Oracle RAC cluster to manage global resources

LMON maintains instance membership within Oracle RAC. The process detects instance transitions and performs reconfiguration of GES and GCS resources.

See Also: Oracle Real Application Clusters Administration and Deployment Guide

Database instances, Oracle ASM instances, Oracle RAC

LMSn

Global Cache Service Process

Manages resources and provides resource control among Oracle RAC instances

LMS, where n is 0-9 or a-z, maintains a lock database for Global Cache Service (GCS) and buffer cache resources. This process receives, processes, and sends GCS requests, block transfers, and other GCS-related messages.

See Also: Oracle Real Application Clusters Administration and Deployment Guide

Database instances, Oracle ASM instances, Oracle RAC

LREG

Listener Registration Process

Registers the instance with the listeners

LREG notifies the listeners about instances, services, handlers, and endpoint.

Database instances, Oracle ASM instances, Oracle RAC

LSP0

Logical Standby Coordinator Process

Schedules transactions for Data Guard SQL Apply

LSP0 is the initial process created upon startup of Data Guard SQL Apply. In addition to managing LogMiner and Apply processes, LSP0 is responsible for maintaining inter-transaction dependencies and appropriately scheduling transactions with applier processes. LSP0 is also responsible for detecting and enabling run-time parameter changes for the SQL Apply product as a whole.

Database instances, Data Guard

LSP1

Logical Standby Dictionary Build Process

Performs a logical standby dictionary build on a primary database

The LSP1 process is spawned on a logical standby database that is intended to become the new primary database. A logical standby database becomes a primary database because of switchover or failover. The dictionary is necessary for logical standby databases to interpret the redo of the new primary database.

Database instances, Data Guard

LSP2

Logical Standby Set Guard Process

Determines which database objects will be protected by the database guard

The LSP2 process is created as needed during startup of SQL Apply to update the list of objects that are protected by the database guard.

Database instances, Data Guard

Lnnn

Pooled Server Process

Handles client requests in Database Resident Connection Pooling

In Database Resident Connection Pooling, clients connect to a connection broker process. When a connection becomes active, the connection broker hands off the connection to a compatible pooled server process. The pooled server process performs network communication directly on the client connection and processes requests until the client releases the server. After being released, the connection is returned to the broker for monitoring, leaving the server free to handle other clients.

See Also: Oracle Database Concepts

Database instances, Database Resident Connection Pooling

MARK

Mark AU for Resynchronization Coordinator Process

Marks ASM allocation units as stale following a missed write to an offline disk

MARK essentially tracks which extents require resynchronization for offline disks. This process runs in the database instance and is started when the database instance first begins using the Oracle ASM instance. If required, MARK can also be started on demand when disks go offline in the Oracle ASM redundancy disk group.

Database instances, Oracle ASM instances

MMAN

Memory Manager Process

Serves as the instance memory manager

This process performs the resizing of memory components on the instance.

Database instances, Oracle ASM instances

MMNL

Manageability Monitor Lite Process

Performs tasks relating to manageability, including active session history sampling and metrics computation

MMNL performs many tasks relating to manageability, including session history capture and metrics computation.

Database instances, Oracle ASM instances

MMON

Manageability Monitor Process

Performs or schedules many manageability tasks

MMON performs many tasks related to manageability, including taking Automatic Workload Repository snapshots and performing Automatic Database Diagnostic Monitor analysis.

Database instances, Oracle ASM instances

Mnnn

MMON Slave Process

Performs manageability tasks on behalf of MMON

Mnnn performs manageability tasks dispatched to them by MMON. Tasks performed include taking Automatic Workload Repository snapshots and Automatic Database Diagnostic Monitor analysis.

Database instances, Oracle ASM instances

MRP0

Managed Standby Recovery Process

Coordinates the application of redo on a physical standby database

MRP0 is spawned at the start of redo apply on a physical standby database. This process handles the extraction of redo and coordinates the application of that redo on a physical standby database.

See Also: Oracle Data Guard Concepts and Administration

Database instances, Data Guard

MSnn

LogMiner Worker Process

Reads redo log files and translates and assembles into transactions

Multiple MSnn processes can exists, where n is 0-9 or a-Z. A minimum of three MSnn processes work as a group to provide transactions to a LogMiner client, for example, a logical standby database or a database capture. There may be more than one such group, for example, multiple capture processes configured for either local or downstream capture in a database.

Database instances, Logical Standby, Oracle Streams, XStream Outbound servers, Oracle GoldenGate

Nnnn

Connection Broker Process

Monitors idle connections and hands off active connections in Database Resident Connection Pooling

In Database Resident Connection Pooling, clients connect to a connection broker process. When a connection becomes active, the connection broker hands off the connection to a compatible pooled server process. The pooled server process performs network communication directly on the client connection and processes requests until the client releases the server. After being released, the connection is returned to the broker for monitoring, leaving the server free to handle other clients.

See Also: Oracle Database Concepts

Database instances, Database Resident Connection Pooling

NSSn

Network Server SYNC Process

Transfers redo from current online redo logs to remote standby destinations configured for SYNC transport

NSSn can run as multiple processes, where n is 1-9 or A.

See Also: Oracle Data Guard Concepts and Administration

Database instances, Data Guard

NSVn

Data Guard Broker NetSlave Process

Performs broker network communications between databases in a Data Guard environment

NSVn is created when a Data Guard broker configuration is enabled. There can be as many NSVn processes (where n is 0- 9 and A-U) created as there are databases in the Data Guard broker configuration.

Database instances, Data Guard

OCFn

ASM CF Connection Pool Process

Maintains a connection to the Oracle ASM instance for metadata operations

 

Database instances, Oracle ASM instances

OFSD

Oracle File Server Background Process

Serves file system requests submitted to an Oracle instance

This background process listens for new file system requests, both management (like mount, unmount, and export) and I/O requests, and executes them using Oracle threads.

Database instances, Oracle RAC

Onnn

ASM Connection Pool Process

Maintains a connection to the Oracle ASM instance for metadata operations

Onnn slave processes are spawned on demand. These processes communicate with the Oracle ASM instance.

Database instances, Oracle ASM instances

PING

Interconnect Latency Measurement Process

Assesses latencies associated with communications for each pair of cluster instances

Every few seconds, the process in one instance sends messages to each instance. The message is received by PING on the target instance. The time for the round trip is measured and collected.

Database instances, Oracle ASM instances, Oracle RAC

PMON

Process Monitor

Monitors the other background processes and performs process recovery when a server or dispatcher process terminates abnormally

PMON periodically performs cleanup of all the following:

  • Processes that died abnormally

  • Sessions that were killed

  • Detached transactions that have exceeded their idle timeout

  • Detached network connections which have exceeded their idle timeout

In addition, PMON monitors, spawns, and stops the following as needed:

  • Dispatcher and shared server processes

  • Job queue processes

  • Pooled server processes for database resident connection pooling

  • Restartable background processes

See Also: Oracle Database Concepts and Oracle Database Net Services Administrator's Guide

Database instances, Oracle ASM instances, Oracle ASM Proxy instances

Pnnn

Parallel Query Slave Process

Perform parallel execution of a SQL statement (query, DML, or DDL)

Parallel Query has two components: a foreground process that acts as query coordinator and a set of parallel slaves (Pnnn) that are background processes. These background processes are spawned or reused during the start of a parallel statement. They receive and perform units of work sent from the query coordinator.

The maximum number of Pnnn processes is controlled by the initialization parameter PARALLEL_MAX_SERVERS. Slave processes are numbered from 0 to the PARALLEL_MAX_SERVERS setting. If the query is a GV$ query, then these background processes are numbered backward, starting from PZ99.

Database instances, Oracle ASM instances

PRnn

Parallel Recovery Process

Performs tasks assigned by the coordinator process performing parallel recovery

PRnn serves as a slave process for the coordinator process performing parallel media recovery and carries out tasks assigned by the coordinator. The default number of these processes is based on number of CPUs.

Database instances

PSP0

Process Spawner Process

Spawns Oracle background processes after initial instance startup

 

Database instances, Oracle ASM instances

QMNC

Non-sharded queue master process

Monitors AQ

QMNC is the non-sharded queue master process responsible for facilitating various background activities required by AQ and Oracle Streams: time management of messages, management of nonpersistent queues, cleanup of resources, and so on. QMNC dynamically spawns Qnnn processes as needed for performing these tasks.

Note that if the AQ_TM_PROCESSES initialization parameter is set to 0, this process will not start. The database writes the following message to the alert log: WARNING: AQ_TM_PROCESSES is set to 0. System might be adversely affected.

Database instances Advanced Queueing

QMnn

AQ Master Class Process

Per instance per AQ Master Class Process

Each of this type of process represents a single class of work item such as AQ notification, queue monitors, and cross process.

Database instances Advanced Queueing

Qnnn

AQ Server Class Process

Per AQ Master Class server process

Each server class process acts on behalf of an AQ master class process. This relationship is maintained until the master requires services of a particular service process. Once released, the server class processes are moved to a free server pool.

Database instances Advanced Queueing

RBAL

ASM Rebalance Master Process

Coordinates rebalance activity

In an Oracle ASM instance, it coordinates rebalance activity for disk groups. In a database instances, it manages Oracle ASM disk groups.

Database instances, Oracle ASM instances

RCBG

Result Cache Background Process

Handles result cache messages

This process is used for handling invalidation and other messages generated by server processes attached to other instances in Oracle RAC.

Database instances, Oracle RAC

RECO

Recoverer Process

Resolves distributed transactions that are pending because of a network or system failure in a distributed database

RECO uses the information in the pending transaction table to finalize the status of in-doubt transactions. At timed intervals, the local RECO attempts to connect to remote databases and automatically complete the commit or rollback of the local portion of any pending distributed transactions. All transactions automatically resolved by RECO are removed from the pending transaction table.

See Also: Oracle Database Concepts and Oracle Database Net Services Administrator's Guide

Database instances

RM

RAT Masking Slave Process

Extracts and masks bind values from workloads like SQL tuning sets and DB Replay capture files

This background process is used with Data Masking and Real Application Testing.

Database instances

RMON

Rolling Migration Monitor Process

Manages the rolling migration procedure for an Oracle ASM cluster

The RMON process is spawned on demand to run the protocol for transitioning an ASM cluster in and out of rolling migration mode.

Oracle ASM instance, Oracle RAC

RMSn

Oracle RAC Management Process

Performs manageability tasks for Oracle RAC

RMSn performs a variety of tasks, including creating resources related to Oracle RAC when new instances are added to a cluster.

See Also: Oracle Real Application Clusters Administration and Deployment Guide

Database instances, Oracle RAC

Rnnn

ASM Block Remap Slave Process

Remaps a block with a read error

A database instance reading from an Oracle ASM disk group can encounter an error during a read. If possible, Oracle ASM asynchronously schedules a Rnnn slave process to remap this bad block from a mirror copy.

Oracle ASM instances

RPnn

Capture Processing Worker Process

Processes a set of workload capture files

RPnn are worker processes spawned by calling DBMS_WORKLOAD_REPLAY.PROCESS_CAPTURE(capture_dir,parallel_level). Each worker process is assigned a set of workload capture files to process.

Worker processes execute in parallel without needing to communicate with each other. After each process is finished processing its assigned files, it exits and informs its parent process.

The number of worker processes is controlled by the parallel_level parameter of DBMS_WORKLOAD_REPLAY.PROCESS_CAPTURE. By default, parallel_level is null. Then, the number of worker processes is computed as follows:

SELECT VALUE 
FROM   V$PARAMETER 
WHERE  NAME='cpu_count';

When parallel_level is 1, no worker processes are spawned.

Database instances

RPOP

Instant Recovery Repopulation Daemon

Responsible for re-creating and/or repopulating data files from snapshot files and backup files

The RPOP process is responsible for re-creating and repopulating data files from snapshots files. It works with the instant recovery feature to ensure immediate data file access. The local instance has immediate access to the remote snapshot file's data, while repopulation of the recovered primary data files happens concurrently. Any changes in the data are managed between the instance's DBW processes and RPOP to ensure the latest copy of the data is returned to the user.

Database instances

RSM0

Data Guard Broker Worker Process

Performs monitoring management tasks related to Data Guard on behalf of DMON

The process is created when a Data Guard broker configuration is enabled.

Database instances, Data Guard

RSMN

Remote Slave Monitor Process

Manages background slave process creation and communication on remote instances in Oracle RAC

This background process manages the creation of slave processes and the communication with their coordinators and peers. These background slave processes perform tasks on behalf of a coordinating process running in another cluster instance.

Database instances, Oracle RAC

RVWR

Recovery Writer Process

Writes flashback data to the flashback logs in the fast recovery area

RVWR writes flashback data from the flashback buffer in the SGA to the flashback logs. RVWR also creates flashback logs and performs some tasks for flashback log automatic management.

Database instances, Flashback Database

SAnn

SGA Allocator

Allocates SGA

A small fraction of SGA is allocated during instance startup. The SAnn process allocates the rest of SGA in small chunks. The process exits upon completion of SGA allocation.

The possible processes are SA00 - SAzz.

Database instances

SCCn

ASM Disk Scrubbing Slave Check Process

Performs Oracle ASM disk scrubbing check operation

SCCn acts as a slave process for SCRB and performs the checking operations. The possible processes are SCC0-SCC9.

Oracle ASM instances

SCRB

ASM Disk Scrubbing Master Process

Coordinates Oracle ASM disk scrubbing operations

SCRB runs in an Oracle ASM instance and coordinates Oracle ASM disk scrubbing operations.

Oracle ASM instances

SCRn

ASM Disk Scrubbing Slave Repair Process

Performs Oracle ASM disk scrubbing repair operation

SCRn acts as a slave process for SCRB and performs the repairing operations. The possible processes are SCR0-SCR9.

Oracle ASM instances

SCVn

ASM Disk Scrubbing Slave Verify Process

Performs Oracle ASM disk scrubbing verify operation

SCVn acts as a slave process for SCRB and performs the verifying operations. The possible processes are SCV0-SCV9.

Oracle ASM instances

SMCO

Space Management Coordinator Process

Coordinates the execution of various space management tasks

This background process coordinates the execution of various space management tasks, including proactive space allocation and space reclamation. SMCO dynamically spawns slave processes (Wnnn) to implement these tasks.

Database instances

SMON

System Monitor Process

Performs critical tasks such as instance recovery and dead transaction recovery, and maintenance tasks such as temporary space reclamation, data dictionary cleanup, and undo tablespace management

SMON performs many database maintenance tasks, including the following:

  • Creates and manages the temporary tablespace metadata

  • Reclaims space used by orphaned temporary segments

  • Maintains the undo tablespace by onlining, offlining, and shrinking the undo segments based on undo space usage statistics

  • Cleans up the data dictionary when it is in a transient and inconsistent state

  • Maintains the SCN to time mapping table used to support Oracle Flashback features

In an Oracle RAC database, the SMON process of one instance can perform instance recovery for other instances that have failed.

SMON is resilient to internal and external errors raised during background activities.

See Also: Oracle Database Concepts

Database instances

Snnn

Shared Server Process

Handles client requests in the shared server architecture

In the shared server architecture, clients connect to a dispatcher process, which creates a virtual circuit for each connection. When the client sends data to the server, the dispatcher receives the data into the virtual circuit and places the active circuit on the common queue to be picked up by an idle shared server. The shared server then reads the data from the virtual circuit and performs the database work necessary to complete the request. When the shared server must send data to the client, the server writes the data back into the virtual circuit and the dispatcher sends the data to the client. After the shared server completes the client request, the server releases the virtual circuit back to the dispatcher and is free to handle other clients.

Several initialization parameters relate to shared servers. The principal parameters are: DISPATCHERS, SHARED_SERVERS, MAX_SHARED_SERVERS, LOCAL_LISTENER, REMOTE_LISTENER.

See Also: Oracle Database Concepts

 

TEMn

ASM disk Test Error Emulation Process

Emulates I/O errors on Oracle ASM disks through named events

I/O errors can be emulated on Oracle ASM disk I/O through named events. The scope can be the process, instance, or even cluster. Optionally, a set of AUs can be chosen for error emulation.

Oracle ASM instances

TTnn

Redo Transport Slave Process

Ships redo from current online and standby redo logs to remote standby destinations configured for ASYNC transport

TTnn can run as multiple processes, where nn is 00 to ZZ.

See Also: Oracle Data Guard Concepts and Administration

Database instances, Data Guard

VBGn

Volume Background Process

Communicates between the Oracle ASM instance and the operating system volume driver

VBGn handles messages originating from the volume driver in the operating system and sends them to the Oracle ASM instance.

VBGn can run as multiple processes, where n is 0-9.

Oracle ASM instances, Oracle ASM Proxy instances

VDBG

Volume Driver Process

Forwards Oracle ASM requests to perform various volume-related tasks

VDBG handles requests to lock or unlock an extent for rebalancing, volume resize, disk offline, add or drop a disk, force and dismount disk group to the Dynamic Volume Manager driver.

Oracle ASM instances, Oracle ASM Proxy instances

VKRM

Virtual Scheduler for Resource Manager Process

Serves as centralized scheduler for Resource Manager activity

VKRM manages the CPU scheduling for all managed Oracle processes. The process schedules managed processes in accordance with an active resource plan.

Database instances

VKTM

Virtual Keeper of Time Process

Provides a wall clock time and reference time for time interval measurements

VKTM acts as a time publisher for an Oracle instance. VKTM publishes two sets of time: a wall clock time using a seconds interval and a higher resolution time (which is not wall clock time) for interval measurements. The VKTM timer service centralizes time tracking and offloads multiple timer calls from other clients.

Database instances, Oracle ASM instances

VMB0

Volume Membership Process

Maintains cluster membership on behalf of the Oracle ASM volume driver

This process membership in the cluster as an I/O-capable client on behalf of the Oracle ASM volume driver.

Oracle ASM instances, Oracle ASM Proxy instances

VUBG

Volume drive Umbilicus Background

Relays messages between Oracle ASM instance and Oracle ASM Proxy instance that is used by ADVM (for ACFS)

 

Oracle ASM instances, Oracle ASM Proxy instances

Wnnn

Space Management Slave Process

Performs various background space management tasks, including proactive space allocation and space reclamation

Wnnn processes are slave processes dynamically spawned by SMCO to perform space management tasks in the background. These tasks include preallocating space into locally managed tablespace and SecureFiles segments based on space usage growth analysis, and reclaiming space from dropped segments. At most 10 Wnnn slaves can run on one database instance. After being started, the slave acts as an autonomous agent. After it finishes task execution, it automatically picks up another task from the queue. The process terminates itself after being idle for a long time.

Database instances

XDMG

Exadata Automation Manager

Initiates automation tasks involved in managing Exadata storage

XDMG monitors all configured Exadata cells for state changes, such as a bad disk getting replaced, and performs the required tasks for such events. Its primary tasks are to watch for inaccessible disks and cells and when they become accessible again, and to initiate the ASM ONLINE operation. The ONLINE operation is handled by XDWK.

Oracle ASM instances, Exadata

XDWK

Exadata Automation Manager

Performs automation tasks requested by XDMG

XDWK gets started when asynchronous actions such as ONLINE, DROP, and ADD an Oracle ASM disk are requested by XDMG. After a 5 minute period of inactivity, this process will shut itself down.

Oracle ASM instances, Exadata

Xnnn

ASM Disk Expel Slave Process

Performs Oracle ASM post-rebalance activities

This process expels dropped disks after an Oracle ASM rebalance.

Oracle ASM instances