Oracle Architectural（Oracle 体系结构）！！！

 

The Oracle server consists of an Oracle instance and an Oracle database.
Oracle 服务器包括一个Oracle 例程和一个Oracle 数据库。

 

Oracle instance: An Oracle instance consists of the System Global Area (SGA) memory structure and the background processes used to manage a database.Always opens one and only one database.The instance can open and use only one database at a time.
Oracle 例程：Oracle 例程由系统全局区(SGA) 内存结构和用于管理数据库的后台进程组成。始终打开一个，并且只打开一个数据库。例程一次只能打开和使用一个数据库。

 

Oracle database: An Oracle database consists of operating system files.An Oracle database consists of three file types:Data files containing the actual data in the database.Redo logs containing a record of changes made to the database to enable recovery of the data in case of failures.Control files containing information necessary to maintain and verify database integrity.
Oracle 数据库：Oracle 数据库包含操作系统文件。Oracle 数据库包含以下三类文件：数据文件，包含数据库中的实际数据。重做日志文件，包含数据库的更改记录，可以在出现故障时恢复数据。控制文件，包含维护和验证数据库完整性所需的信息。

 

The SGA consists of several memory structures:Shared pool,Database buffer cache,Redo log buffer.Shared Pool——The shared pool is used to store the most recently executed SQL statements and the most recently used data definitions.It consists of two key performance-related memory structures:Library cache,Data dictionary cache.Library Cache,The library cache stores information about the most recently used SQL and PL/SQL statements.Data Dictionary Cache，The data dictionary cache is a collection of the most recently used definitions in the database.Database Buffer Cache——The database buffer cache stores copies of data blocks that have been retrieved from the data files.Redo Log Buffer Cache——The redo log buffer cache records all changes made to the database data blocks.Its primary purpose is recovery.
SGA 包括以下几种内存结构：共享池，数据库缓冲区高速缓存，重做日志缓冲区。共享池——用于存储：最近执行的SQL 语句，最近使用的数据定义。它包括以下两个与性能相关的关键内存结构：库高速缓存，数据字典高速缓存。库高速缓存，存储有关最近使用的SQL 和PL/SQL 语句的信息。数据字典高速缓存，数据库中最近使用的定义的集合。数据库缓冲区高速缓存——存储已从数据文件中检索到的数据块的副本。重做日志缓冲区——记录对数据库数据块所做的全部更改。主要用于恢复。