Oracle 11G 程式講解

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:

Database instance

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.

ASM instance, 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 instance, Oracle RAC

APnn

Logical Standby / Streams 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.

See Also:

Database instance, Data Guard, Oracle Streams

ARBn

ASM Rebalance Process

Rebalances data extents within an ASM disk group

Possible processes are ARB0-ARB9 and ARBA.

ASM instance

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 LGWR cannot reuse and overwrite an online redo log group until it has been archived.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: and

Database instance

ASMB

ASM Background Process

Communicates with the ASM instance, managing storage and providing statistics

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

Database and ASM instances

ASnn

Logical Standby / Streams Apply Process Reader Server 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 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.

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

Database instance

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:

Database instance

Bnnn

ASM Blocking Slave Process for GMON

Performs maintenance actions on 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 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.

ASM instance

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: and

Database instance

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.

See Also:

Database and ASM instances

CPnn

Streams 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 view for information about this background process.

See Also:

Database instance, Oracle Streams

CSnn

Streams Propagation Sender Process

Sends LCRs to a propagation receiver

The propagation sender process name is CSnn, 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 instance, 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 instance, 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:

Database instance

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:

Database instance

DBWn

Database Writer Process

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

The primary responsibility of DBWn is to write data blocks to disk. DBWn also handles checkpoints, file open synchronization, and logging of Block Written records.

In many cases the blocks that DBWn writes are scattered throughout the disk. Thus, the writes tend to be slower than the sequential writes performed by LGWR. DBWn 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 DBWn processes (DBW0-DBW9 and DBWa-DBWz). The database selects an appropriate default setting for this parameter or adjusts a user-specified setting based on the number of CPUs and processor groups.

See Also: and

Database instance

DIA0

Diagnostic Process

ASM and Database instances

DIAG

Diagnostic Capture Process

ASM and Database 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 instance, 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:

Database instance, 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:

Database instance, shared servers

DRnn

ASM Disk Resynchronization Slave Process

Resynchronizes the contents of an offline disk

When a disk online SQL command is issued on a disk or disks that are offline, ASM spawns DRnn. Depending on the load, more than one slave may be spawned.

ASM Instance

DSKM

Slave Diskmon Process

Acts as the conduit between the database, 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.

ASM instance, 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 instance

EMNC

EMON Coordinator Process

Coordinates database event management and notifications

EMNC coordinates event management and notification activity in the database, including Streams Event Notifications, Continuous Query Notifications, and Fast Application Notifications.

Database and ASM 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 and ASM 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 Advanced Application Developer's Guide

Database and 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 and 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 instance, 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 and ASM instances, Oracle RAC

GEN0

General Task Execution Process

Performs required tasks including SQL and DML

Database and ASM instances

GMON

ASM Disk Group Monitor Process

Monitors all mounted ASM disk groups

GMON monitors all the disk groups mounted in an 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.

ASM instance

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 process disabled, an error is returned.

See Also:

Database instance, 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 instance

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 instance, Data Guard

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 instance

LCK0

Instance Enqueue Background Process

Manages global enqueue requests and cross-instance broadcasts

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

Database and ASM instances, Oracle RAC

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: and

Database and ASM instances

LMD0

Global Enqueue Service Daemon 0 Process

Manages incoming remote resource requests from other instances

LMD0 processes enqueue resources managed under Global Enqueue Service. In particular, LMD0 processes incoming enqueue request messages and controls access to global enqueues. It also performs distributed deadlock detections.

Database and 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 and 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:

Database and 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:

Database and 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 runtime parameter changes for the SQL Apply product as a whole.

Database instance, 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 by means of switchover or failover. The dictionary is necessary for logical standby databases to interpret the redo of the new primary database.

Database instance, 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 instance, 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:

Database instance, 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 ASM instance. If required, MARK can also be started on demand when disks go offline in the ASM redundancy disk group.

Database and ASM instances

MMAN

Memory Manager Process

Serves as the instance memory manager

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

Database and 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 and 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 and 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 and 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:

Database instance, 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. There may be more than one such group, for example, Downstream Capture sessions.

Database instance, Logical Standby, Oracle Streams

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:

Database instance, Database Resident Connection Pooling

NSAn

Redo Transport NSA1 Process

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

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

See Also:

Database instance, Data Guard

NSSn

Redo Transport NSS1 Process

Acts as a slave for LGWR when SYNC transport is configured for a remote standby destination

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

See Also:

Database instance, 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 instance, Data Guard

OCFn

ASM CF Connection Pool Process

Maintains a connection to the ASM instance for metadata operations

Database and ASM instances

Onnn

ASM Connection Pool Process

Maintains a connection to the ASM instance for metadata operations

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

Database and 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 and 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

PMON is also responsible for registering information about the instance and dispatcher processes with the network listener.

See Also: and

Database and ASM 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 carry out 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 and 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 instance

PSP0

Process Spawner Process

Spawns Oracle background processes after initial instance startup

Database and ASM instances

QMNC

AQ Coordinator Process

Monitors AQ

QMNC is 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 instance, Advanced Queuing

Qnnn

AQ Server Class Process

Performs various AQ-related background task for QMNC

Qnnn acts as a slave process for QMNC and carry out tasks assigned by QMNC. The number of these processes is dynamically managed by QMNC based on load.

Database instance

RBAL

ASM Rebalance Master Process

Coordinates rebalance activity

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

Database and 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 instance, 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: and

Database instance

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:

Database instance, Oracle RAC

Rnnn

ASM Block Remap Slave Process

Remaps a block with a read error

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

ASM instance

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 instance

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 instance, 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 instance, 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 instance, Flashback Database

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 instance

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:

Database instance

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:

Database instance, shared servers

TEMn

ASM disk Test Error Emulation Process

Emulates I/O errors on ASM disks through named events

I/O errors can be emulated on 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.

ASM instance

VBGn

Volume Background Process

Communicates between the 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 ASM instance.

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

ASM instance

VDBG

Volume Driver Process

Forwards 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.

ASM instance

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 instance

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 and ASM instances

VMB0

Volume Membership Process

Maintains cluster membership on behalf of the ASM volume driver

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

ASM instance

Vnnn

ASM Volume I/O Slave Process

Initializes ASM volume contents during creation

This process is responsible for initializing the ASM volume during creation.

ASM instance

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 instance

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.

ASM instance, Exadata

XDWK

Exadata Automation Manager

Performs automation tasks requested by XDMG

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

ASM instance, Exadata

Xnnn

ASM Disk Expel Slave Process

Performs ASM post-rebalance activities

This process expels dropped disks at the end of an ASM rebalance.

ASM instance