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This article will explain in detail how the oracle background process is, and the content of the article is of high quality, so the editor will share it for you as a reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

The oracle background process starts with the startup of the instance, and they mainly maintain the stability of the database, which is equivalent to the managers and internal service personnel in an enterprise. They do not provide services directly to users.

One: write database write-- data to DBWR

Function: synchronize the modified data in SGA to a disk file. Ensure that there are enough free blocks in the Buffer Cache.

PS: if LGWR fails, DBWR will not listen to the CKPT command to strike, because Oracle will write the log buffer to the log file before writing the data cache data to disk, and patiently wait for it to be completed before completing the action of brushing memory to disk. This is the so-called recording of everything.

Trigger conditions: 1. Checkpoint CKPT

2. A service process did not find a free block within the set time.

3. Wake up automatically every three seconds.

Setting: DB_WRITER_PROCESS is used to define the number of DBWn processes. (the commit command only writes record changes to the log file, not the modified data to the data file)

Second: write log write:LGWR-- log files (model workers, a very important and busy process)

Function: write the log content in log buffer to the online log file, freeing up the buffer space for log users.

Trigger conditions: 1. The user issues the commit command. (called quick commit mechanism (fast commit) in oracle): writes a record in redo log buffer to a log file and writes a submitted record

2. Wake up regularly in three seconds.

3. The log buffer log buffer exceeds 1Comp3, or the number of logs exceeds 1m.

4. DBWR process trigger: the DBWn view writes dirty data blocks to disk, first detects whether his relevant redo records are written to the online log file, and if not, notifies the LGWR process. In oracle, it is called write ahead: redo records are written to disk before data records.

5. Switching between online log files will also trigger LGWR.

Three: checkpoint:CKPT- checkpoint event

Function: maintain the consistency of the database. The data file of the detection point is consistent with the content in SGA. This is not a separate process, but should work with the first two processes. DBWR writes dirty data and triggers the LGWR process.

CKPT updates the checkpoint record in the control file. The trigger time of CKPT is controlled by setting a parameter adjustment. The parameter is FAST_START_MTTR_TARGET.

Trigger condition: log switching (log switch) triggers a checkpoint.

Four: process monitor:PMON-- maintains the user process monitor

Function: 1, find that the user process terminates abnormally, and clean up. Release occupied resources. (clean up locks used by abnormally terminated users)

2. Register the instance dynamically with the listener.

Trigger condition: it will be awakened regularly, and other processes will wake it up actively.

Fifth, system monitor:SMON-- instance maintenance process system monitor

Function: 1. Responsible for instance recovery, Roll Forward to the state where the instance is closed, and redo it using the log process after the last checkpoint. This includes committed and uncommitted transactions. Open the database and Roll Back: roll back uncommitted transactions. (oracle promises that data will not be lost after commit, and now we can get a rough idea of how to achieve this promise and the balance between data security and database performance.)

2. Responsible for cleaning up the temporary period to free up space

Trigger condition: be awakened periodically or actively awakened by other transactions.

6: LCKn is only applicable to RAC databases, and a maximum of 10 processes (LCK0,LCK1,...,LCK9) can be used for blocking between instances.

Seven: archive:ARCH-- archiving operation

Function: copy full online log files to the archive directory when log switching occurs. (when LGWR writes a log and needs to be overwritten, trigger the ARCH process to transfer the log file and copy it out to form an archived log file to avoid log loss.)

Trigger condition: awakened by LGWR during log switching.

Setting: LOG_ARCHIVE_MAX_PROCESSES can set the number of ARCH when oracle starts.

Eight: Distributed Database Recovery-RECO for the recovery of distributed database

An application spans multiple databases and needs to be committed successfully before the transaction will be successful, otherwise all will be rolled back.

These are the eight most core, most important, and most useful processes, and some are listed below.

IX: major processes of manageability monitor:MMON--AWR

Function: 1. Collect the necessary statistical data of AWR and write the statistical data to disk. 10g is saved in the SYSAUX table space.

2. Generate server--generated alarm

Write the statistics in shared pool to disk every hour, or the shared pool occupies more than 15%.

Ten: manageability monitor light:MMNL: lightweight MMON

Eleven: memory manager:MMAN: automatic content management

Purpose: check AWR performance information every minute and use that information to determine the best distribution of SGA components.

Setting: STATISTICS_LEVEL: statistical level

Total SGA_TARGET:SGA size

Twelve: job queue coordinator:CJQ0-- database timing tasks

Oracle's job queue management depends on the execution of background processes, which perform data refreshes and other regular jobs. Schedule the process CJQ0, select the jobs to be executed, and extend the job queue process (J000-J999) to execute these jobs

Thirteen: recover writer:RVWR

Purpose: to provide logging for flashback database. Writes the previous mirror of the data block to the log.

Fourteen: change tarcking writer:CTWR

Function: track the change of data block and record the address of data block in change_tracking file file. Incremental backups of RMAN will use this file to determine which blocks have changed and to back up.

About how the oracle background process is shared here, I hope the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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