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This article mainly shows you "what the architecture is like in oracle". The content is simple and clear. I hope it can help you solve your doubts. Let the editor lead you to study and learn what the architecture is like in oracle.

Oracle servers and instances

The oracle instance consists of sga and background processes.

Sga includes shared pool, database high-speed buffer, redo log high-speed buffer, java pool, stream pool, large pool, etc.

Background processes are monitored by the system (SMON), process monitoring (PMON), database writing process (DBWR), log writing process (LGWR), checkpoint (CKPT), archiving (ARCH) and so on. Database instance startup must start the first five processes, otherwise the database cannot be used properly.

Oracle server consists of instances, database files, user processes, and server processes that users link to the database, pga

Data file (physical structure)

Control file (crontrol files) maintains database integrity information

The redo log file (redo log files) records changes that occur in the database and is used for recovery in the event of a failure

Data file (datafiles) actual data of the database

Parameter file (parameter) defines the characteristics of the database instance, sga size, high-speed buffer size, etc.

Password file (password) stores the password of all users who connect to the database with sysdba or sysoper permissions, such as sys. This password is not stored in the database, but in the password file.

Archive log files (archivelog files) offline backup of log files to recover user data in the event of a failure

Shared Pool (shared pool)

Library cache: caches recently used sql and pl/sql statements, and uses the LRU algorithm to clear statements that have not been used for a period of time

Data dictionary cache: caches the definitions of data files, tables, indexes, columns, users, permission information and other data objects; for example, user name and user rights need to be resolved to execute sql, and data dictionary cache can cache this information to speed up query. The main function is to cache data dictionary information to shorten query time.

Database high speed buffer

The function of the database cache is to cache the block information that the user recently read from the data file or the information that the user modified data is rewritten back to the data file; if the user modified data has not been submitted to the database, it is called dirty data. The simple understanding is to cache the statements executed by the user and put them in memory without direct physical reading, because memory must be faster than physical disk reading.

Redo log cache

When the user executes the DML and DDL statements, any changes in the data will be written to the redo log high-speed buffer, regardless of before and after the changes, to ensure that the database can be rolled forward or backward for data recovery.

Daichi (Large Pool)

Large pools are optional for sga and are only configured in shared server mode to allocate additional space for glow information between user processes and server processes

Process Global area (PGA)

Pga in dedicated server mode

Pga in shared server mode

Server process (server process)

It is similar to an intermediary, which completes the user's various database service requests, and then returns the database response to the client.

In proprietary server mode, one server process versus one user process

In shared server mode, one server process corresponds to multiple user processes

User process (user process)

A process initiated by an end user accessing a database client link, such as sqlplus,plsql developer

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