SMON - System Monitor process recovers
after instance failure and monitors temporary segments and extents.
SMON in a non-failed instance can also perform failed instance recovery
for other failed RAC instance.
PMON - Process Monitor process
recovers failed process resources. If MTS (also called Shared Server Architecture)
is being utilized.
PMON monitors and restarts any failed dispatcher or server processes.
In RAC, PMON’s role as service registration agent is particularly
important.
DBWR - Database Writer or Dirty Buffer
Writer process is responsible for writing dirty buffers from the database block
cache to the database data files.
Generally, DBWR only writes blocks back to the data files on commit,
or when the cache is full and space has to be made for more blocks.
The possible multiple DBWR processes in RAC must be coordinated through
the locking and global cache processes to ensure efficient processing is
accomplished.
LGWR - Log Writer process is
responsible for writing the log buffers out to the redo logs. I n RAC, each RAC
instance has its own LGWR process that maintains that instance’s thread of redo
logs.
ARCH - (Optional) Archive process
writes filled redo logs to the archive log location(s). In RAC, the various
ARCH processes can be utilized to ensure that copies of the archived redo logs
for each instance are available to the other instances in the RAC setup should
they be needed for recovery.
CKPT - Checkpoint process writes
checkpoint information to control files and data file headers.
Pnnn - (Optional) Parallel Query
Slaves are started and stopped as needed to participate in parallel query
operations.
CQJ0 - Job queue controller process
wakes up periodically and checks the job log.
If a job is due, it spawns Jnnn processes to handle jobs.
Jnnn - (Optional) Job processes used
by the Oracle9i job queues to process internal Oracle9i jobs. The CQJ0 process
controls it automatically.
QMN - (Optional) Advanced Queuing
process is used to control the advanced queuing jobs.
Snnn - (Optional) Pre-spawned shared
server processes are used by the multi-threaded server (MTS) process to handle
connection requests from users, and act as connection pools for user processes.
These user processes also handle disk reads from database datafiles into
the database block buffers.
Dnnn - (Optional) Dispatcher process
for shared server (MTS) - It accepts connection requests and portions them out
to the pre-spawned server processes.
MMON – This process performs various
manageability-related background tasks, for example:
MMNL - This process performs frequent
and lightweight manageability-related tasks, such as session history capture
and metrics computation.
MMAN - is used for internal database
tasks that manage the automatic shared memory. MMAN serves as the SGA
Memory Broker and coordinates the sizing of the memory components.
RBAL - This process coordinates
rebalance activity for disk groups in an Automatic Storage Management instance.
ORBn - performs the actual rebalance
data extent movements in an Automatic Storage Management instance.
There can be many of these at a time, called ORB0, ORB1, and so forth.
OSMB - is present in a database
instance using an Automatic Storage Management disk group.
It communicates with the Automatic Storage Management instance.
FMON - The database communicates with
the mapping libraries provided by storage vendors through an external
non-Oracle Database process that is spawned by a background process called
FMON. FMON is responsible for managing the mapping information.
When you specify the FILE_MAPPING initialization parameter for mapping
data files to physical devices on a storage subsystem, then the FMON process is
spawned.
LMON - The Global Enqueue Service
Monitor (LMON) monitors the entire cluster to manage the global enqueues and
the resources.
LMON manages instance and process failures and the associated recovery
for the Global Cache Service (GCS) and Global Enqueue Service (GES).
In particular, LMON handles the part of recovery associated with global
resources. LMON-provided services are also known as cluster group services (CGS)
LMDx - The Global Enqueue Service
Daemon (LMD) is the lock agent process that manages enqueue manager service
requests for Global Cache Service enqueues to control access to global enqueues
and resources.
The LMD process also handles deadlock detection and remote enqueue
requests.
Remote resource requests are the requests originating from another
instance.
RAC Background Processes
LMSx - The Global Cache Service
Processes (LMSx) are the processes that handle remote Global Cache Service
(GCS) messages. Real Application Clusters software provides for up to 10 Global
Cache Service Processes.
The number of LMSx varies depending on the amount of messaging traffic
among nodes in the cluster. The LMSx handles the acquisition interrupt and
blocking interrupt requests from the remote instances for Global Cache Service
resources. For cross-instance consistent read requests, the LMSx will create a consistent
read version of the block and send it to the requesting instance. The LMSx also
controls the flow of messages
to remote instances.
LMSn - The LMSn processes
handle the blocking interrupts from the remote instance for the Global Cache
Service resources by:
·
Managing the resource requests
and cross-instance call operations for the shared resources.
·
Building
a list of invalid lock elements and validating the lock elements during
recovery.
·
Handling the global lock deadlock
detection and Monitoring for the lock conversion timeouts
LCKx -
This process manages the global enqueue requests and the cross-instance
broadcast. Workload is automatically shared and balanced when there are
multiple Global Cache Service Processes (LMSx).
DIAG: Diagnosability Daemon –
Monitors the health of the instance and captures the data for instance process
failures.
