The background processes of the Oracle instance manage memory structures, asynchronously perform I/O to write data to a file on a disk, and perform general maintenance tasks. Each background process has a separate task but works with the other processes as well.
The post provides information on some new and some pre-existing background processes in 10G which may be unfamiliar.
|CTWR||Change Tracking Writer|
|MMNL||Memory Monitor Light|
|M000||MMON background slave|
|CJQn||Job Queue monitoring|
|RBAL||ASM rebalancing process|
|ARBx||Process managed by RBAL to do the actual rebalancing of ASM|
|ASMB||Process used to provide information to and from the Cluster Synchronization Services used by ASM to manage the disk resources|
– SGA Background Process
– The Automatic Shared Memory Management feature uses a new background process named Memory Manager (MMAN).
– MMAN serves as the SGA Memory Broker and coordinates the sizing of the memory components. The SGA Memory Broker keeps track of the sizes of the components and pending resize operations
– “Flashback database” is a new feature introduced in 10g.
– Flashbacking a database means going back to a previous database state.
– The Flashback Database feature provides a way to quickly revert an entire Oracle database to the state it was in at a past point in time.
– This is different from the traditional point in time recovery.
– A new background process Recovery Writer ( RVWR) introduced which is responsible for writing flashback logs which stores pre-image(s) of data blocks.
– One can use Flashback Database to back out changes that:
- Have resulted in logical data corruptions.
- Are a result of user error.
– This feature is not applicable for recovering the database in case of media failure.
– The time required for flashbacking a database to a specific time in past is DIRECTLY PROPORTIONAL to the number of changes made and not on the size of the database.
These are job queue processes which are spawned as needed by CJQ0 to complete scheduled jobs. This is not a new process.
This is a new process Change Tracking Writer (CTWR) which works with the new block changed tracking features in 10g for fast RMAN incremental backups.
The Memory Monitor Light (MMNL) process is a new process in 10g which works with the Automatic Workload Repository new features (AWR) to write out full statistics buffers to disk as needed.
– The Manageability Monitor (MMON) process was introduced in 10g and is associated with the Automatic Workload Repository new features used for automatic problem detection and self-tuning.
– MMON writes out the required statistics for AWR on a scheduled basis.
MMON background slave (m000) processes.
This is the Job Queue monitoring process which is initiated with the job_queue_processes parameter. This is not new.
This is the ASM related process that performs rebalancing of disk resources controlled by ASM.
– These processes are managed by the RBAL process and are used to do the actual rebalancing of ASM controlled disk resources.
– The number of ARBx processes invoked is directly influenced by the asm_power_limit parameter.
– The ASMB process is used to provide information to and from the Cluster Synchronization Services used by ASM to manage the disk resources.
– It is also used to update statistics and provide a heartbeat mechanism.
Understanding Oracle Background Processes
New Background Processes In Oracle Database 12c