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Step 5 - Oracle Background Processes

Learn Oracle - Oracle Background Processes

Oracle creates a set of background processes for an instance that interact with each other and with the operating system to manage memory structure, asynchronously perform I/O to write data to disk, and do general housekeeping. The background processes consolidate functions that would otherwise be handled by multiple Oracle programs running for each user process. They asynchronously perform I/O and monitor other Oracle processes to provide increased parallelism for better performance and reliability.

There are many background processes and not all may be present depending upon the features that are being used in the database. The most common background processes, and ones that most directly affect Oracle DBA, are the following:

Background Process Description

Database Writer (DBWn)

The database writer writes modified blocks from the database buffer cache to the files on disk. Oracle allows a maximum of 20 database writer processes.

Log Writer (LGWR)

The log writer process writes redo log entries to disk. Redo log entries are generated in the redo log buffer of the SGA and the log writer process writes the redo log entries sequentially into an online redo log file.

Checkpoint At specific times, all modified database buffers in the SGA are written to the datafiles by a database writer process (DBWn). This event is called a checkpoint. The checkpoint process is responsible for signalling DBWn at checkpoints and updating all of the datafiles and control files of the database to indicate the most recent checkpoint.

System Monitor (SMON)

The system monitor performs crash recovery when a failed instance starts up again.

Process Monitor (PMON)

The process monitor performs process recovery when a user process fails. It is responsible for cleaning up the cache and freeing resources that the failed process was using.

Archiver (ARCn)

When the database is running in archive log mode, one or more archiver processes copy the redo log files to archival storage when the log files are full or a log switch occurs.
Oracle Tutorial - BLOGS

STEP 5 - Next Topics
This step discusses starting and stopping the database instance, and managing initialization parameters.Learn Oracle DBA Step 5 by clicking links below:
Instance Memory StructureConfiguring Network
Oracle Background ProcessesBackground processes
Accessing the Database
Shuting down and Restarting the instance and Database
Viewing and Modifying Initialization
Managing Memory Parameters
Oracle Database - PODCASTS
More Tutorials on Oracle dba ...

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Source : Oracle Documentation | Return to Learn Oracle

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