[Oracle] limit)

Guidance:
Oracle has various restrictions (limit). A clear understanding of these restrictions can help us better use Oracle and understand oracle.
This is the first article in the Oracle restrictions series. It mainly introduces some basic limits (sessions, processes) set by Oracle initialization parameters)
Key word: ORA-00018, ORA-00020
1.Sessions
Among the restrictions set by initialization parameters, the most well-known estimates are sessions and processes.
The sessions parameter specifies the number of concurrent users that can exist in an instance at the same time, or the number of concurrent users that can log on to the database at the same time. Generally, when setting this number, we need to consider how many concurrent users we may connect to the database at the same time, add the number of background processes, and multiply the number of processes with 1.1.
For example, it is estimated that 100 users may connect to the database in the system at least, so your session should be
(100 10) * 1.1 = 121
When the concurrent user connected to the database reaches this value and a new session is connected, an error is reported.
00018,000 00, "Maximum number of sessions exceeded"
// * Cause: All session State objects are in use.
// * Action: increase the value of the sessions initialization parameter.
2.Processes
The processes parameter is similar to sessions.
The processes parameter specifies the number of processes that the instance can run simultaneously at the OS level. Based on the same settings as sessions, when setting processes, we should also consider how many concurrent users we may have connected to the database at the same time, and add the number of background processes.
Of course, in the MTS (Shared Server) configuration, this value will indeed be different. It should be the maximum number of processes (max_shared_servers) of the Shared Server for common background processes, and the maximum number of dispatcher processes (max_dispatchers ).
In addition, since Oracle exists in the form of a single process on the window platform, the processes parameter is changed to a limit on the number of threads in the Oracle process.
When Oracle needs to start a new process and the process parameter has been reached, an error is returned:
00020,000 00, "Maximum number of processes (% s) Exceeded"
// * Cause: All process state objects are in use.
// * Action: increase the value of the processes initialization parameter.
Tag: Oracle

This article is transferred from
Http://www.cnblogs.com/wllyy189/archive/2008/06/12/1218206.html