Background
Process Information
Here's a list of background processes:
- SMON
The System Monitor carries out a crash
recovery when a crashed insance is started up again. In a
Real Application Clusters database, the SMON process of one instance
can perform instance recovery for other instances that have failed.
SMON also cleans up temporary segments that are no longer in use and
recovers dead transactions skipped during system failure and instance
recovery because of file-read or offline errors. These transactions are
eventually recovered by SMON when the tablespace or file is brought
back online.
- PMON
The process monitor performs process recovery when a user process
fails. PMON is responsible for cleaning up the cache and freeing
resources that the process was using. PMON also checks on the
dispatcher processes and server processes and restarts them if they
have failed.
- DBWR
The Database Writer writes modified
blocks (dirty
blocks) from the database buffer
to the datafiles. The amount of DBWn Processes to start is
determined by the initialization
parameter DB_WRITER_PROCESSES. DBWR also writes the actual
SCN with the Block.
- LGWR
The Log Writer writes the redo
log buffer from the SGA to the online
redo log files.
- MRP
Managed recovery process: the process that applies archived redo log to
the standby
database.
- RFS
The remote file server process on the standby
database receives archived redo logs from the primary
database.
- RECO
The recoverer process is used to resolve distributed transactions that
are pending due to a network or system failure in a distributed
database. 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.
- CKPT
The Checkpoint Process reqularly
initiates a checkpoint which uses DBWR to write all
dirty blocks back to the datafiles, thus synchronizing the database.
Since a Checkpoint records the current SCN, in a recovery only redo
records with a SCN higher than that of the last checkpoint need to be
applied.
- ARCH
The Archiver Process archives redo log files
if ARCHIVELOG
is enabled.
- Dnnn
The Dispatcher Process is used in a shared
server environment.
- Snnn
The Shared Server Process is used in a shared
server environment.
- LMON
The lock manager.
- LMD0
- QMNn
AQ Time Manager. A queue monitor process which monitors the message
queues. Used by Oracle Streams Advanced Queuing.
- TRWR
Trace
writer
- WMON
The wakeup monitor process.
- LCKnnn
Inter-instance locking process.
- SNPnnn
The snapshot process.
- DMON
The Data
Guard Broker process.
MMAN (10g)
SGA Background Process
The Automatic Shared Memory Management feature uses a new background
process named Memory Manager (MMAN). MMAN serves as the SGA
Memory Broker and coordinates the sizing of the memory components. The
SGA Memory Broker keeps track of the sizes of the components and
pending resize operations
RVWR (10g)
Flashback database
-----------------------------
- This a new feature introduced in 10g.
- Flashbacking a database means going back to a previous database state.
- The Flashback Database feature provides a way to quickly revert an
entire Oracle database to the state it was in at a past point in time.
- This is different from traditional point in time recovery.
- A new background process Recovery Writer ( RVWR) introduced which is
responsible for writing flashback logs which stores pre-image(s) of
data blocks
- One can use Flashback Database to back out changes that:
- Have resulted in logical data corruptions.
- Are a result of user error.
- This feature is not applicable for recovering the database in case of
media failure.
- The time required for flashbacking a database to a specific time in
past is DIRECTLY PROPORTIONAL to the number of changes made and not on
the size of the database.
Jnnn (10g)
These are job queue processes which are spawned as needed by CJQ0 to
complete scheduled jobs. This is not a new process.
CTWR (10g)
This is a new process Change Tracking Writer (CTWR) which works with
the new block changed tracking features in 10g for fast RMAN
incremental backups.
MMNL (10g)
The Memory Monitor Light (MMNL) process is a new process in 10g which
works with the Automatic Workload Repository new features (AWR) to
write out full statistics buffers to disk as needed.
MMON (10g)
The memory monitor (MMON) process was introduced in 10g and is
associated with the Automatic Workload Repository new features used for
automatic problem detection and self-tuning. MMON writes out the
required statistics for AWR on a scheduled basis.
CJQn (10g)
This is the Job Queue monitoring process which is initiated with the
job_queue_processes parameter. This is not new. More Info DOCID=222190.1