1-ORACLE体系结构.ppt

User Process A database user who needs to request information from the database must first make a connection with the Oracle server. The connection is requested using a database interface tool, such as SQL*Plus, and beginning the user process. The user process does not interact directly with the Oracle server. Rather it generates calls through the user program interface (UPI), which creates a session and starts a server process. Server Process Once a user has established a connection, a server process is started to handle the user processes requests. A server process can be either a dedicated server process or a shared server process. In a dedicated server environment, the server process handles the request of a single user process. Once a user process disconnects, the server process is terminated. In a shared server environment, the server process handles the request of several user processes. The server process communicates with the Oracle server using the Oracle Program Interface (OPI). Note: Allocation of server process in a dedicated environment versus a shared environment is covered in further detail in the Oracle9i Performance Tuning course. Background Processes The Oracle architecture has five mandatory background processes that are discussed further in this lesson. In addition to the mandatory list, Oracle has many optional background process that are started when their option is being used. These optional processes are not within the scope of this course, with the exception of the ARCn background process. Following is a list of some optional background processes: RECO: Recoverer QMNn: Advanced Queuing ARCn: Archiver LCKn: RAC Lock Manager—Instance Locks LMON: RAC DLM Monitor—Global Locks LMDn: RAC DLM Monitor—Remote Locks CJQ0: Snapshot Refresh Dnnn: Dispatcher Snnn: Shared Server Pnnn: Parallel Query Slaves Database Writer The server process records changes to rollback and data blocks in the buffer cache. Database Writer (DBWn) writes the dirty buffers