The processes in Oracle are divided into three categories: User processes, service processes, background processes. The background process with the start of the instance started, they are mainly to maintain the stability of the database, the equivalent of an enterprise managers and internal service personnel. They do not provide services directly to users.
A: Database write--Data write: Synchronizes the modified data in the SGA to a disk file. Ensure that there is sufficient number of free blocks in the buffer cache. Trigger conditions: 1, checkpoint 2, a service process in the set time has not found free Block 3, every three seconds automatically wake up once. Settings: Db_writer_process is used to define the number of dbwn processes. (The commit command simply writes the record modification to the log file, instead of writing the modified data to the data file)
Two: Log WRITE:LGWRLog file Write function: Write the log contents in log buffer to the online log file, releasing the log user buffer space. Trigger condition: 1, the user issued a commit command. (called Fast commit in Oracle): Writes a record in redo log buffer to a log file, writes a committed record 2, three seconds, and wakes up periodically. 3, log buffer more than 1/3, or the number of logs more than 1M. 4. DBWR process trigger: DBWN View writes dirty chunks to disk first detects if his related redo records are written to the online log file, and if not, notifies the LGWR process. Become an advance write mechanism in Oracle (write ahead): Redo records are written to disk before data records
Three: Checkpoint:ckpt-Checkpoint event function: maintains database consistency status. Point-in-time data files are consistent with the content in the SGA, which is not a separate process to work with the first two processes. DBWR writes dirty data while triggering the LGWR process. CKPT update the checkpoint record in the control file. Trigger condition: Log switch will trigger a checkpoint.
Four: Process Monitor:pmon--Maintain user process function: 1, the user process is found to terminate abnormally, and to clean up. Frees up resource usage. (Clean up the lock used by the user to terminate the exception) 2, to the listener dynamic registration instance. Trigger Condition: The timer is awakened, and the other process will wake it up actively.
V: System monitor:smon--Instance Maintenance Process function: 1, in charge of the instance recovery, roll Forward back to the status of the instance shutdown, using the log process after the last checkpoint redo. This includes both committed and uncommitted transactions. Open the database for rollback (roll back): Rollback of uncommitted transactions. (The data is not lost after Oracle commits commit, and we now have a general idea of how to implement this commitment, as well as a balanced selection between data security and database performance.) 2, is responsible for cleaning up the temporary segment to release the space trigger condition: periodically wake up or be awakened by other affairs actively.
Six: Archive:arcn--Archive operation: When log switching occurs, the full online log file is copied to the archive directory. Trigger condition: The log switch is LGWR awakened. Settings: Log_archive_max_processes can set the number of ARCN when Oracle starts.
Seven: Manageability Monitor:mmon--awr main Process function: 1, collect the data required by AWR, write statistics to disk. Saved in the Sysaux table space in 10g. 2. Generate server--generated Alarm every hour the statistics in the shared pool are written to disk, or the shared pool occupies more than 15%.
Eight: Manageability Monitor light:MMNL: Lightweight Mmon
Nine: Memory Manager:mman:Automated Content Management: Check awr performance information every minute and based on this information to determine the optimal distribution of SGA components. Setting: Statistics_level: Statistics level SGA_TARGET:SGA Total size
10: Job Queue coordinator:cjq0--Database timed Tasks
11: Recover WRITER:RVWRRole: Provides logging for flashback database. Writes the front image of the data block to the log.
12: Change tarcking WRITER:CTWRFunction: Trace the change of data block and record the address of block to change_tracking file. An incremental backup of Rman will use this file to determine that the data blocks have changed and are backed up. These are the more common background processes in Oracle, not all processes. Where DBWN,ARCN can set the amount of time the database starts. These processes can be more than one in the system.
Oracle Background Process 2
