Oracle RAC Background Processes in 11g
Oracle RAC 11g has come up with some good new background processes. Which we will discuss in this session
ABMR – auto block media recovery background process – Filters duplicate BMR requests and performs flood control. When a request of block media recovery comes to ABMR, then ABMR spawns BMRn slave processes to perform block media recovery dynamically. repairing of corrupted blocks on primary site by obtaining the same block from standby site and the vice versa on active standby from primary site. Get terminated when idle for long time along with slave processes. It is BMRn slave processes which actually fetches blocks from real time standby database.
DBRM – database resource manager background process – Sets resource plans if resource plan is enabled otherwise this process is idle. It sets resource plans and performs various operations related to enforcement of those resource plans.
DIA0..9 – diagnostic process 0 to 9 background processes – this process is responsible for dead lock resolution and hand detection. this process triggers another background process called as DIAG to perform diagnostic tasks such as performing diagnostic dumps. DIAG is also responsible for execution of global oradebug commands. DIAG also performs diagnostic dumps as requested by other processes or during instance termination.
EMNC – event monitor coordinator background process – This process coordinates event management and notification activity including streams event notification, continuous query notification, Fast application notifications. EMNC spaws EMON slave processes E000…4. These processes work on the system notifications in parallel, offering a capability to process a larger volume of notifications, a faster response time, and a lower shared memory use for staging notifications.
FBDA – flash back data archiver background process – When a table data get commited by transactions the pre image of the effected rows of table from undo tablespace is stored by this process into flashback data archives so that historical pre images of data for a long term can be querried. this process also maintains metadata of current rows and tracks how much data has been updated. this process also responsible for space, partitioning of tablespaces and retention of flashback data archives. this process keeps track of how far archiving of tracked transactions has progressed.
GEN0 – general task execution background process – the main goal of this process is to offload those processes which potentially blocking other processes. these required tasks are for sql and DML. Other processes request GEN0 to perform those tasks which can safely be run at background and that other process can concentrate on its task and GEN0 notifies back once given task is done.
Innn – Disk and Tape I/O Slave processes background process – these processes are spawned by other background processes such as DBWR, LGWR or an RMAN backup session. I/O slave process can be configured on platforms where asynchronous I/O support is not available. These slaves are started by setting the corresponding slave enable parameter in the server parameter file. The I/O slaves simulate the asynchronous I/O behavior when the underlying platform does not have native support for asynchronous I/O.
Lnnn – Pooled Server Background processes – handles client requests in Database Resident connection pooling. In Database Resident Connection Pooling, clients connect to a connection broker process. When a connection becomes active, the connection broker hands off the connection to a compatible pooled server process. The pooled server process performs network communication directly on the client connection and processes requests until the client releases the server. After being released, the connection is returned to the broker for monitoring, leaving the server free to handle other clients.
Nnnn – Connection broker background processes – monitors idle connections and hands off active connections in database resident connection pooling. In Database Resident Connection Pooling, clients connect to a connection broker process. When a connection becomes active, the connection broker hands off the connection to a compatible pooled server process. The pooled server process performs network communication directly on the client connection and processes requests until the client releases the server. After being released, the connection is returned to the broker for monitoring, leaving the server free to handle other clients.
RCBG – result cache background process – This process is used for handling invalidation and other messages generated by server processes attached to other instances in Oracle RAC
RPnn – Replay processing/Capture processing background process –
RPnn are worker processes spawned by calling DBMS_WORKLOAD_REPLAY.PROCESS_CAPTURE(capture_dir,parallel_level). Each worker process is assigned a set of workload capture files to process.
Worker processes execute in parallel without needing to communicate with each other. After each process is finished processing its assigned files, it exits and informs its parent process.
The number of worker processes is controlled by the parallel_level parameter of DBMS_WORKLOAD_REPLAY.PROCESS_CAPTURE. By default, parallel_level is null. Then, the number of worker processes is computed as follows:
When parallel_level is 1, no worker processes are spawned.
SMCO – space management coordinator background process – this process spawns Wnnn slave processes to do space management tasks like space reclamation and space allocation.
VKRM – Virtual scheduler for resource manager background process – VKRM manages the CPU scheduling for all managed Oracle processes. The process schedules managed processes in accordance with an active resource plan.
VKTM – Virtual keeper of time process – VKTM acts as a time publisher for an Oracle instance. VKTM publishes two sets of time: a wall clock time using a seconds interval and a higher resolution time (which is not wall clock time) for interval measurements. The VKTM timer service centralizes time tracking and offloads multiple timer calls from other clients.