Oracle Partial background process

1.PMON: Background process

Responsible for clean-up after an abnormally aborted connection

Pmon will roll back uncommitted work, release the lock, and release the SGA resource previously allocated for the failed process

Responsible for monitoring other background processes and restarting these background processes or appropriate termination instances if necessary

2.LREG: Monitor Registration process

Responsible for registering the DB instance and the service in the listener.

If the listener is in a running state, Lreg communicates with the listener and passes the relevant parameters to the listener

If the listener does not start, Lreg will periodically try to contact the listener to register itself with the listener.

3.SMON: System Monitor

Used to do all the "system-level" tasks.

. Clean Up temporary table space

. Merge free space (dictionary-managed tablespace)

Transactions for file recovery activities that were not previously available

Perform instance recovery for failed nodes in RAC

. Cleanup obj$ obj$ is a bottom-level data dictionary table. The rows that are not needed in the table are cleaned up by the Smon process.

The Administrative revocation Section Smon will be responsible for implementing the automatic upper and lower line of the undo segment, as well as shrinking the Undo section.

. Rollback Segment Offline

4.RECO: Distributed Database Recovery

Some transactions may remain prepared due to a crash or loss of connection during two-phase commit, which is the process of recovering these transactions

5.CKPT: Checkpoint Process

The implementation of checkpoints is primarily the work of the DBWN process

Assists in the process of actually running checkpoints to update the file header of the data file

6.DBWn: Data block writer

Background process responsible for writing dirty blocks to disk----in order to make more space in the cache, or to push checkpoints

If he writes the block fast enough not to release the buffer quickly, you will see the number of both wait events and the wait time start increasing for both the free buffer waits and the write Completel waits

36 Dbwn can be set in 11g

100 dbwn can be set in 12c

7.LGWR: Log writer

Responsible for flushing the contents of the Redo log buffers in the SGA to disk.

LGWR Working Conditions

Every 3 seconds.

When a commit or rollback is initiated

LGWR is told to log file switching

Redo Log buffer is 1/3 full, or already contains 1MB of buffered disk

8.ARCn: Archive Process

When LGWR fills an online redo log file, it copies it to another location.

Archived redo log files can be used for full media recovery

Online redo logs are used to "fix" data files when a power-down occurs

Archive redo logs are used to "remediate" data files in the event of a hard disk failure

The online redo log file is typically copied to at least two other locations.

The archive redo log file is copied by another process to a three-level storage device---tape.

9.DIAG: Diagnostic process

Dedicated to RAC, responsible for monitoring the overall situation of the instance, and capturing the information needed to process the instance failure

10.FBDA: Flash back Data archive process

After the transaction commits, the undo generated by the transaction is read and the changes made by the transaction are rolled back. These rows are then recorded in the Flashback data archive after the rollback.

11.DBRM: Database Explorer Process

To implement a resource plan that is configured for a DB instance.

12.gen0: Common task Execution process

Provides a process for the database to perform common tasks, and the primary goal of the process is to share some of the processes that could cause blocking in the process and put them in the background.

Oracle Partial background process