A user process is created and maintained to execute the software code of an application program. it is a shADOw process created automatically to facilitate communication between the user and the server process.
Server process handle requests from connected user process. A server process is in charge of communicating with the user process and interacting with Oracle carry out requests of the associated user process.
Dedicated server configuration and multi-threaded server configuration.
In a dedicated server configuration a server process handles requests for a single user process.
In a multi-threaded server configuration many user processes share a group of server process.
A configuration for loosely coupled systems where multiple instance share a single physical database is called parallel server.
Database writer writes modified blocks from the database buffer cache to the data files.
Process monitor (pmon) performs process recovery when a user process fails pmon is responsible for cleaning up the cache and freeing resources that the process was using pmon also checks on dispatcher and server processes and restarts them if they have failed.
Archiver (arch) copies the on-line redo log files to archival storage when they are full. arch is active only when a database's redo log is used in archivelog mode.
Recover (reco) is used to resolve distributed transactions that are pending due to a network or system failure in a distributed database. At timed intervals,the local reco attempts to connect to remote databases and automatically ...
Dispatcher (dnnn) process is responsible for routing requests from connected user processes to available shared server processes and returning the responses back to the appropriate user processes.
Atleast one dispatcher process is created for every communication protocol in use.
Lock (lckn) are used for inter-instance locking when the Oracle parallel server option is used.
Though a single lck process is sufficient for most parallel server systemsupto ten locks (lck0,....Lck9) are used for inter-instance locking.