Different Oracle Background Processes

Which are the different oracle background processes?


The important oracle background processes are :
- Database Writer(DBWR), 
- Log Writer(LGWR), 
- System Monitor(SMON), 
- Process Monitor(PMON), 
- Archiver(ARCH),
- CheckPoint(CKPT),
- Dispatcher Processes.
Database Writer (DBWR) 

Database Writer process (DBWR) writes buffers to datafiles. DBWR is an Oracle background process responsible for buffer cache management.

Log Writer (LGWR) 

The Log Writer process (LGWR) writes the redo log buffer to a redo log file on disk. LGWR is an Oracle background process responsible for redo log buffer management. LGWR writes all redo entries that have been copied into the buffer since the last time it wrote. LGWR writes one contiguous portion of the buffer 
to disk. LGWR writes  A commit record when a user process commits a transaction  Redo buffers every three seconds Redo buffers when the redo log buffer is one-third full Redo buffers when the DBWR process writes modified buffers to disk

Checkpoint (CKPT) 

When a checkpoint occurs, Oracle must update the headers of all datafiles to indicate the checkpoint. In normal situations, this job is performed by LGWR. However, if checkpoints significantly degrade system performance (usually, when there are many datafiles), you can enable the Checkpoint process (CKPT) to separate the work 
of performing a checkpoint from other work performed by LGWR, the Log Writer process(LGWR).

System Monitor (SMON) 

The System Monitor process (SMON)performs instance recovery at instance start up. SMON is also responsible for cleaning up temporary segments that are no longer in use; it also coalesces contiguous free extents to make larger blocks of free space available 

Process Monitor (PMON) 

The Process Monitor (PMON) performs process recovery when a user process fails. PMON is responsible for cleaning up the cache and freeing resources that the process was using. For example, it resets the status of the active transaction table, releases locks, and removes the process ID from the list of active processes. 

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