Oracle 10g Background processes

There are a large number of new background processes in Oracle 10g, however there are just 5 that are vital for the Database to work.

5 Old and Vital background processes

- SMON (System Monitor): Performs instance recovery, cleans up temporary segments
no longer in use and recovers dead transactions, coalesce free extents in the database.

- DBWR (Database Writer): This process in on charge of writing to the DB files.

- CKPT (Checkpoint): This process is on charge of executing checkpoint

- PMON (Process Monitor): Recovers when a user process fails, clean up cache and free
resources, it also monitors dispatchers and server processes.

- LGWR (Log Writer): This process is on charge of write to the redo log files

New Background processes

ASM:

- ARBn : (ASM) Rebalance working process , it rebalances extents.

- ORBn: Rebalance ASM data extent movements. There can be many of this at the same time.

- RBAL : This is the ASM Rebalance Master disk manager, open all disks under each disk group and make them
available to the various clients. It also creates the rebalance plan to move extents.

- OSMB: (ASM) Helps to manage the drive storage.

- ASMB: (ASM) Responsible to communicate the database Instance to the ASM Instance, provides the heartbeat to the ASM instance.

Server Side Optional

- RECO: Helps to Recover distributed Transactions.

- ORA_CJQ0_: Job queue coordinator , checks the log and spawn J### processed

- QMNC: AQ Coordinator, used to manage Oracle Streams Advance Queuing.

- ARCH, ARCn: Copies redo logs to archive logs destination.

- CTWR: Block Change Tracking Writer.

- ORA_D###_: Oracle Dispatchers processed

- ORA_J###_: Job queue process

- ORA_MMAN_: Memory manager, used for the manage of the automatic shared memory.

- ORA_MMNL_: Helps collecting metrics and information about sessions.

- ORA_MMON_: On charge of collecting stats.

- ORA###_: Dedicated server (user process).

- ORA_RVWR_: Recovery Writer (Flashback Database).

- ORA_S###_: Oracle Shared Server Process (Multi Threaded Server)

- ORA_P###_: Parallel Query Slaves Process

- ORA_LNS#_: Network Server.

Other Processes

- ORA_AQ_: Sends notifications when messages arrive into the queues (Advance Queue).

- ORA_Q###_: Queue Process.

- ORA_DMON_: Data Guard Broker Process.

- ORA_SNP###_: Snapshot process (Data Guard).

- ORA_TRWR_: Advance Queuing Time Manager.

- ORA_WMON_: Wakeup monitor process.

Undocumented Server Side Extra

- ORA_FMON_: Manage mapping information when using FILE_MAPPING

Standby Mode

- ORA_LSP0_: Logical Standby

- ORA_LSP1_: Dictionary build process for Logical Standby

- ORA_LSP2_: Set Guard Standby information for logical Standby.

- ORA_DMON_: Data Guard Broker Monitor Process.

- ORA_RSM#_: Data Guard Broker Resource Guard process.

- ORA_INSV_: Data Guard Broker Instance slave process

- ORA_NSV#_: Data Guard Broker NetSlave Process.

- ORA_MRP0_: Managed Recovery process for Data Guard.

- ORA_RFS_: Remote File Server process (Data Guard) receives archived redo from primary.

Real Application Cluster

- The following processes are unique to a RAC environment. You will not see them otherwise.

* Lock monitor (LMON) process: The LMON process monitors all instances in a cluster to detect the failure of an instance. It then facilitates the recovery of the global locks held by the failed instance. It is also responsible for reconfiguring locks and other resources when instances leave or are added to the cluster (as they fail and come back online, or as new instances are added to the cluster in real time).

* Lock manager daemon (LMD) process: The LMD process handles lock manager service requests for the global cache service (keeping the block buffers consistent between instances). It works primarily as a broker sending requests for resources to a queue that is handled by the LMSn processes. The LMD handles global deadlock detection/resolution and monitors for lock timeouts in the global environment.

* Lock manager server (LMSn) process: As noted earlier, in a RAC environment, each instance of Oracle is running on a different machine in a cluster, and they all access, in a read-write fashion, the same exact set of database files. To achieve this, the SGA block buffer caches must be kept consistent with respect to each other. This is one of the main goals of the LMSn process In earlier releases of Oracle Parallel Server (OPS) this was accomplished via a ping. That is, if a node in the cluster needed a read-consistent view of a block that was locked in exclusive mode by another node, the exchange of data was done via a disk flush (the block was pinged). This was a very expensive operation just to read data. Now, with the LMSn, this exchange is done via very fast cache-to-cache exchange over the clusters¿ high-speed connection. You may have up to ten LMSn processes per instance.

* Lock (LCK0) process: This process is very similar in functionality to the LMD process described earlier, but it handles requests for all global resources other than database block buffers.

- CM: Cluster Manager , it maintains the status of the nodes and instances across the cluster.

- GCS: Global Cache Service

- GES: Global Enqueue Service daemon

- GMS: Group Membership Service

- NM: Node Monitor

-NPIC: Network Inter-process communication

- ORA_PSP0_: Process spawner, allows Oracle PL/SQL embedded in HTML (PLUG IN)

- CSS (Cluster Synchronization Services): Cluster management and node monitoring, monitors
ASM

- CRS (Cluster Register Service):

- ORA_EMNO_: Event Monitor Process

- ORA_DIAG_: Diagnosability daemon (DIAG) process: The DIAG process is used exclusively in a RAC environment. It is responsible for monitoring the overall ¿health¿ of the instance, and it captures information needed in the processing of instance failures.