This post provides information on new background processes introduced in 11g.
ACMS (atomic controlfile to memory service)
This per-instance process is an agent that contributes to ensuring a distributed SGA memory update is either globally committed on success or globally aborted in the event of a failure in an Oracle RAC environment.
DBRM (database resource manager)
This process is responsible for setting resource plans and other resource manager related tasks.
DIA0 (diagnosability process 0)
This process (only 0 is currently being used) is responsible for hang detection and deadlock resolution.
DIAG (diagnosability) process
This process performs diagnostic dumps and executes global oradebug commands.
EMNC (event monitor coordinator)
This process is the background server process used for database event management and notifications.
FBDA (flashback data archiver process)
This process archives the historical rows of tracked tables into flashback data archives. Tracked tables are tables which are enabled for flashback archive. When a transaction containing DML on a tracked table commits, this process stores the pre-image of the rows into the flashback archive. It also keeps metadata on the current rows.
FBDA is also responsible for automatically managing the flashback data archive for space, organization, and retention and keeps track of how far the archiving of tracked transactions has occurred.
GTX0-j (global transaction) processes
This process provides transparent support for XA global transactions in an Oracle RAC environment. The database autotunes the number of these processes based on the workload of XA global transactions. Global transaction processes are only seen in an Oracle RAC environment.
This process performs proxy I/O to an ASM metafile when a disk goes offline.
This process marks ASM allocation units as stale following a missed write to an offline disk.
SMCO (space management coordinator) process
This process coordinates the execution of various space management related tasks, such as proactive space allocation and space reclamation. It dynamically spawns slave processes (Wnnn) to implement the task.
VKTM (virtual keeper of time)
This process is responsible for providing a wall-clock time (updated every second) and reference-time counter (updated every 20 ms and available only when running at elevated priority).
Some additional Processes not documented in 10G
PZ (PQ slaves used for global Views)
Thes processes are RAC Parallel Server Slave processes, but they are not normal parallel slave processes, PZnn processes (starting at 99) are used to query GV$ views which is done using Parallel Execution on all instances, if more than one PZ process is needed, then PZ98, PZ97,… (in that order) are created automatically.
O00 (ASM slave processes)
A group of slave processes establishes connections to the ASM instance. Through this connection pool database processes can send messages to the ASM instance. For example, opening a file sends the open request to the ASM instance via a slave. However, slaves are not used for long running operations such as creating a file. The use slave (pool) connections eliminate the overhead of logging into the ASM instance for short requests
Slave used to expell disks after diskgroup reconfiguration.
New Background Processes In Oracle Database 10g
ASM background processes in 11gR2
Understanding Oracle Background Processes