Shulou(Shulou.com)06/01 Report--

1.PMON: background process

Responsible for cleaning up after abnormal termination of the connection

PMON rolls back uncommitted work, releases locks, and releases SGA resources previously allocated to failed processes

Responsible for monitoring other background processes and restarting them or terminating instances as appropriate

2.LREG: listen to the registration process

Responsible for registering database instances and services with listeners.

If the listener is running, 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 "system-level" tasks.

. Clean up temporary tablespaces

. Merge free space (dictionary-managed tablespace)

. Restore active transactions for files that were originally unavailable

. Perform instance recovery of failed nodes in RAC

. Cleaning up OBJ$ OBJ$ is an underlying data dictionary table. It is up to the SMON process to clean up rows in the table that are no longer needed.

. The management revocation segment SMON is responsible for implementing the automatic loading and unloading of the revocation segment and shrinking the revocation segment.

. The rollback segment is offline

4.RECO: distributed database recovery

Due to crashes or loss of connections during two-phase commit, some transactions may remain ready, and this process is to restore these transactions.

5.CKPT: checkpoint proc

Implementing checkpoints is mainly the work of the DBWn process

Assist the process of actually running the checkpoint to update the header of the data file

6.DBWn: block writer

The background process responsible for writing dirty blocks to disk-to free up more space in the cache, or to promote checkpoints

If he writes the block not fast enough to release the buffer quickly, he will see that the number and waiting time of free buffer waits and write completel waits wait events begin to increase

36 DBWn can be set in 11g

100C DBWn can be set in 12c

7.LGWR: log writer

Responsible for flushing and outputting the contents of the redo log buffer in SGA to disk.

LGWR working conditions

Every 3 seconds

When a commit or rollback is initiated

When LGWR is told to switch log files

The redo log buffer 1max 3 is full, or a buffer disk that already contains 1MB

8.ARCn: archiving proc

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

Archived redo log files can be used for full media recovery

The online redo log is used to "correct" the data file in the event of a power outage

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

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

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

9.DIAG: diagnostic proc

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

10.FBDA: flashback data archiving process

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

11.DBRM: database Explorer process

To implement resource plans that are configured for a database instance.

12.GEN0: general task execution process

The database is provided with a process to perform common tasks, and the main goal of the process is to share some of the processes that may cause blocking in the process and complete them in the background.

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