My Oracle Notes (2): User Process, Server Process, and Background Process

Various Processes in the Oracle system can be divided into two categories:

1. the user process that executes the application or Oracle tool code ).

2. The Oracle process that executes the Oracle database server code ). This includes server process and background process ).

What is User Process?

When you run an application to interact with an Oracle database (such as a Pro * C program) or an Oracle tool (such as an enterprise manager or SQL * Plus), Oracle createsUser Process(User process) to run the user's application.

 

What is Server Process?

Server Process is used to Process the requests submitted by the User Process connected to the instance. When an application runs on the same machine as an Oracle Server, some User processes and Server processes can be merged into the same Process, even if the system overhead is reduced. Logically speaking, User processes must communicate with Oracle through a Server Process. (However, some User processes and Server processes are merged on the same machine sometimes)

The Server Process created for the User application (or the Process after the combination of User Process and Server Process) can do the following:

(1) Parse and run the SQL statement submitted by the application.

(2) If the data is not found in SGA, read the required data block from the data file on the disk to the data buffer zone (Shared Database Buffers) of SGA ).

(3) return the execution result of the SQL statement in the form that the application can process.

 

What is Backgroud Process?

To provide services to multiple users and ensure system performance, multiple Oracle processes, called Background, exist in a multi-process Oracle System.

An Oracle instance may contain multiple background processes, which may not always be running. A large number of background processes run in the system.V $ BGPROCESSView to query information about background processes.

The following background processes may run in an Oracle instance:

(1) Data Writing Process Database Writer Process (DBWn)

(2) Log writing Process Log Writer Process (LGWR)

(3) Checkpoint Process (CKPT)

(4) System Monitor Process (SMON)

(5) Process Monitor Process (PMON)

(6) reply to the Process Recoverer Process (RECO)

(7) Job Queue Process

(8) Archiver Process (ARCn)

(9) Queue monitoring Process Queue Monitor Process (QMNn)

(10) Other background processes include MMON, MMNL, MMAN, RBAL, ORBn, and OSMB.

WhereDBWn, PMON, CKPT, LGWR, SMONIs a process that must be started after an instance is started.

Shows how the main background processes interact with each part of the Oracle database: