Background processes are part of the database instance and perform maintenance tasks to operate the database and to maximize performance for multiple users. Each background process performs a unique task, but works with the other processes. Oracle Database creates background processes automatically when you start a database instance. The background processes that are present depend on the features that you're using database. When you start a database instance, mandatory background processes automatically start. You can start optional background processes later as required.

Mandatory background processes are present in all typical database configurations. These processes run by default in a read/write database instance that was started with a minimally configured initialization parameter file. A read-only database instance disables some of these processes. Mandatory background processes include the process monitor (PMON), process manager (PMAN), listener registration (LREG), system monitor (SMON), database writer (DBWn), checkpoint (CKPT), manageability monitor (MMON), manageability monitor lite (MMNL), recoverer (RECO), and log writer (LGWR).

Most optional background processes are specific to tasks or features. Some common optional processes include the archiver (ARCn), job queue coordinator (CJQ0), recovery writer (RVWR), flashback data archive (FBDA), and space management coordinator (SMCO).

Worker processes are background processes that perform work on behalf of other processes. These include the dispatcher (Dnnn) and shared server (Snnn) processes.