Oracle 9i Study Notes

Oracle 9i Server

Oracle 9i includes processes, memory structures, files, and other components
The Oracle 9i server is composed of an Oracle instance and an Oracle database.
An Oracle instance is composed of background processes and memory structures. To access data in the database, you must start the Oracle instance before accessing the database. If you start the Oracle instance, the System will automatically allocate a full Area (SGA ), and start the corresponding Oracle background process. The global area of the system is actually a part of the memory, which is automatically allocated by the system to store the database information shared by the database process, the data buffer storage area and the redo log buffer area are composed of three parts.
The shared pool is used to store frequently executed SQL statements and frequently used data dictionaries. The shared pool is composed of a database cache and a data dictionary cache. The database cache area is used to store the most commonly executed SQL statements, also known as the shared SQL area. The content is SQL text, the compiled syntax tree and the execution plan to be used to execute the statement. The data dictionary cache is also called the dictionary cache or data row cache. It is used to store object definition information in frequently-used databases, including database files, tables, indexes, columns, and users, permission and other object information.
The data buffer storage area is mainly used to store frequently used data.
Redo and log buffer record the changes made by the server process to the data files. And the location where the data changes. If the redo log buffer is full, you need to write the content in the redo log buffer to the redo log file, and then record any changes to the data of the service process.
The Oracle background process is mainly used to improve the performance and reliability of the database. It can be used by multiple users. Including SMON, DBWO, CKPT, LGWR, and other processes.
SMON: Short for System Monitor,
DBWO: Abbreviation of Database Writer.
PMON: Process Monitor.
CKPT: the abbreviation of a process Checkpoint.
LGWR: the abbreviation of Log Writer.
 
 
Oracle database file:
A database file consists of an Oracle database and an additional file.
The physical structure of a database refers to various objects and data of a database. The logical structure of a database refers to the collection of operating system files in a database.
Oracle databases include three types of files: data files, redo log files, and control files.
 
Data files contain data dictionaries, indexes, and other types of structures. There must be at least one data file.
Redo log files record any changes made to the database. A database requires at least two redo log files.
The control file contains information used to maintain and verify database integrity. At least one control file