This background process is available starting with Oracle Database 11g Release 2 (11.2.0.2).
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.
Name
Expanded Name
Short Description
Long Description
External Properties
version
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.
Database instance
<a href="../../backup.112/e10642/rcmblock.htm">See Also: Oracle Database Backup and Recovery User's Guide</a>
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 内存服务器原子控制文件
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.仅适用于 RAC 实例中。执行分布式 SGA 更新时，ACMS 可确保在所有实例上发生更新。如果某个实例上的更新失败，此进程也会在所有实例上回滚更新。可将 ACMS 视为两阶段提交协调器进程，用于 RAC 集群中的 SGA 更新。
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.
Database instance, Data Guard, Oracle Streams
<a href="../../server.112/e17069/strms_apply.htm">See Also: Oracle Streams Concepts and Administration</a>
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: Oracle Database Concepts and Oracle Database Administrator's Guide
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)
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.
Applies LCRs to database objects or passes LCRs and user messages to their appropriate apply handlers (Apply Server)
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.
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.
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.
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.
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.
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.
Database instance, Oracle Streams
<a href="../../server.112/e17069/strms_capture.htm">See Also: Oracle Streams Concepts and Administration</a>
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.
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.
<a href="../../backup.112/e10642/rcmbckba.htm">See Also: Oracle Database Backup and Recovery User's Guide</a>
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.
DBRM
Database Resource Manager Process 数据库资源管理器
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.执行资源计划和其他与资源管理器相关的任务,数据库资源管理进程, (The database resource manager process)，负责设置资源计划和其他的资源管理的工作。
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: Oracle Database Concepts and Oracle Database Performance Tuning Guide
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. 执行诊断、转储跟踪文件（如有必要）以及执行全局 oradebug 命令,数据库诊断进程， (The diagnosibility process) ，负责维护管理各种用于诊断的转储文件，并执行oradebug命令。
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.
Database instance, Data Guard
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.
<a href="../../server.112/e40771/concepts.htm">See Also: Oracle Data Guard Broker</a>
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.
Database instance, shared servers
Several initialization parameters relate to shared servers. The principal parameters are: DISPATCHERS, SHARED_SERVERS, MAX_SHARED_SERVERS, LOCAL_LISTENER, REMOTE_LISTENER.
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. 负责oracle 实例、asm实例和磁盘的管理进程之间的io fencing 信息的交换。如果使用SAGE的存储，该进程还负责SAGE存储的一些信息的管理。
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.
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.
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.
FBDA
Flashback Data Archiver Process 闪回数据存档器
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.Oracle Database 11g 提供新的“闪回存档”，用于写入对表所作的更改。此进程将写入闪回存档。Flashback Data Archiver Process (FBDA)
The flashback data archiver process (FBDA)archives historical rows of tracked tables into Flashback Data Archives. When a transaction containing DML on a tracked table commits, this process stores the pre-image of the rows into the Flashback Data Archive. It also keeps metadata on the current rows.
FBDA automatically manages the flashback data archive for space, organization, and retention. Additionally, the process keeps track of how far the archiving of tracked transactions has occurred.
Cleans up Oracle ASM stale FDs on foreground processes
This process cleans up Oracle ASM stale FDs on foreground processes if an Oracle ASM disk is globally closed.
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.
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.
<a href="#sthref4612">GCRn</a>
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
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.用于维护asm磁盘组的磁盘之间的关系。
GTXn
Global Transaction Process 全局事务进程 0
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.在 RAC 集群中，Oracle Database 现在提供改进的 XA 事务处理。此进程协调 XA 事务。如果 XA 上的数据库负载增长，将自动创建更多进程，分别命名为 GTX1、GTX2，直至 GTXJ。
<a href="../../rac.112/e41960/hafeats.htm">See Also: Oracle Real Application Clusters Administration and Deployment Guide</a>
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.
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.
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.
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.
LCK进程就是锁进程，它管理在集群中对同一数据块访问的锁管理。
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.
LMD0
Global Enqueue Service Daemon 0 Process 全局队列服务
LMD:Lock Manager Daemon，锁管理器
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.
Cache Fusion的GES服务的作用就是在节点之间协调对同一数据块的访问次序，进程LMD就是提供GES服务。另外，RAC环境中LMD进程管理各个节点锁资源，生成死锁的trace文件，如：Global Enqueue Services Deadlock detected. More info in file /u01/app/Oracle/diag/rdbms/raclhr/raclhr2/trace/raclhr2_lmd0_19923170.trc.
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.
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.
<a href="../../rac.112/e41960/admcon.htm">See Also: Oracle Real Application Clusters Administration and Deployment Guide</a>
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
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.
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.
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.
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.
Mark AU for Resynchronization Coordinator Process为重新同步协调器标记分配单元
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.当磁盘出现故障时将会脱机，从而导致写入内容丢失。在这种情况下，此进程会将 ASM 分配单元 (AU) 标记为陈旧。当磁盘联机时，陈旧的段将被刷新。MARK：如果有向asm离线磁盘的missed 写请求，该进程将ASM分配的单元的状态标记为stale
FBDA：涉及到flashback-data-archive新特性的一个进程，The flashback data archiver proces。用于将“轨表”(tracked tables)的历史数据进行归档。当“轨表”上的事务提交以后，fbda进程负责将数据的前镜像保存到flashback archive区域。该进程还负责flashback的数据归档的空间管理、分配、保留，跟踪tracked transactions。
MMON performs many tasks related to manageability, including taking Automatic Workload Repository snapshots and performing Automatic Database Diagnostic Monitor analysis.
Mnnn performs manageability tasks dispatched to them by MMON. Tasks performed include taking Automatic Workload Repository snapshots and Automatic Database Diagnostic Monitor analysis.
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.
<a href="../../server.112/e41134/manage_ps.htm">See Also: Oracle Data Guard Concepts and Administration</a>
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.
Monitors idle connections and hands off active connections in 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.
<a href="../../server.112/e41134/toc.htm">See Also: Oracle Data Guard Concepts and Administration</a>
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.
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.
OCFn
ASM CF Connection Pool Process
Maintains a connection to the ASM instance for metadata operations
Onnn
ASM Connection Pool Process
Onnn slave processes are spawned on demand. These processes communicate with the ASM instance.
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.
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: Oracle Database Concepts and Oracle Database Net Services Administrator's Guide
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.
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.
PSP0
Process Spawner Process
Spawns Oracle background processes after initial instance startup
process spawner，用于产生oracle进程
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.
Database instance, Advanced Queuing
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.
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.
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.
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.
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.
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.The Oracle RAC management processes,负责执行Oracle RAC的管理任务，比如RAC相关资源的创建和集群中新实例的添加。
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.
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.
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.
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.
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 空间管理器
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.SMCO 是主空间管理进程，可动态分配和回收空间。它将生成从进程 Wnnn 以执行这些任务。space management coordinator，该进程负责空间管理协调管理工作，负责执行空间的分配和回收。Space Management Coordinator Process (SMCO)
The SMCO process coordinates the execution of various space management related tasks, such as proactive space allocation and space reclamation. SMCO dynamically spawns slave processes (Wnnn) to implement the task.
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.
Snnn
Shared Server Process
Handles client requests in the shared server architecture
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.
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.
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.
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.
VKTM
Virtual Keeper of Time Process 虚拟计时器进程
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.提供时钟时间（每秒钟更新一次）。以提升的优先级运行时，此进程每 20 毫秒更新一次。virtual keeper of time，用于提供wall-clock time，（每秒钟更新一次）。提供每二十毫秒更新一次的reference-time counter，看起来有点类似计时器的功能。
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.
Vnnn
ASM Volume I/O Slave Process
Initializes ASM volume contents during creation
This process is responsible for initializing the ASM volume during creation.
Wnnn
Space Management Slave Process 空间管理工作器进程
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.执行从 SMCO 收到的指令。根据需要生成更多进程，命名为 W000、W001 等。命名为W000，W001，W002.....，由SMCO动态产生执行上述相关任务。
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.
XDWK
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.
Xnnn
ASM Disk Expel Slave Process
Performs ASM post-rebalance activities
This process expels dropped disks at the end of an ASM rebalance.
BWnn
可以有1到100个数据库写进程。前36个数据库写进程是 DBW0-DBW9和DBWa-DBWz。第37到100个数据库写进程是 BW36-BW99。数据库为 DB_WRITER_PROCESSES 参数选择一个恰当的默认配置或者基于 CPU 和处理器组的个数调整用户指定的配置。
12C
FENC
Fence Monitor Process
为使用 Oracle ASM 实例的 RDBMS 实例处理 fence 请求。
IPC0
IPC Service Background Process
IPC0 (IPC Service Background Process) 常见后台服务器的基本消息和基于 IPC (进程间通信)方式的 RDMA 原语。
LDDn
Global Enqueue Service Daemon Helper Slave
LDDn (Global Enqueue Service Daemon Helper Slave) 帮助 LMDn 进程处理各种任务。
这个进程负责维护数据库集群层面的节点关系（Cluster Group Service，CGS），并与其他实例的LMON进程定期进行心跳通信。当节点间出现了通信问题时，这个节点负责完成实例层面的重新配置（reconfiguration）和GES层面的实例恢复。当某一个（或多个）实例离开或加人数据库集群时，这个进程也负责完成实例层面的重新配置。每个数据库实例只会存在一个LMON进程。
