What is a database? The database is a batch of procedures for processing data files. ====================================================== ac 中 数据There are two types of information: user data is data for a particular application (such as customer shipping). System data is the data required by the database system management itself (for example, the name and storage location related to all data files related to the particular database). ====================================================== Database is the cabinet, cabinet The drawer is a table space, the folder in the drawer is a data file, the paper in the folder is a table, and the information written on paper is data. ====================================================== 1) Table space is A collection of one or more data files. 2) The following list space is a must or common in most databases:. Save information required to manage the O R A C L E body and where the data is stored in the system tablespace. The names of these tablespace are fixed. The temporary table space is an area temporarily used in O R A C L E. When a particular event occurs, O R A C L e requires transactions related to these disk space management. . Tool table space Save objects needed for tool software running on the O R A C L e database. The user tablespace stores the user-specific database object. Rolling the rollback segment of the database object in the back table. The application data of the user is stored in the data and index tables. Index is a special type of database object. O R A C L e uses an index to enter a fast data retrieval. 3) Full table scanning (Full Table Scan) refers to each line data of O R A C L E to access a particular object. 4) Recovery (U N D O) Information Save in a dedicated database object called Rollback Segment, which can be returned to the old value when the failure or temporary interworking occurs. ============================================================================================================================================================================================================= === Redo log) is also called Transaction Log, and o Racle records modifications or transactions for databases in these special operating system files.
All modifications made to the database are made in memory. ======================================= ================== 1) The Oracle database consists of two types of files:. Combined with data files that constitute table spaces. Combined with data files that constitute the redo log series. 2) A database must have at least two redo logs. 3) The reform log contains all transaction entries that occur in the database. 4) Reduction logs are often also known as transaction logs. 5) In order to prevent data loss, the transaction log must be used, the function of the transaction log is: recovered data when an unexpected fault occurs. 6) Oracle Databases can be run in both modes:. All transaction logs will be saved in ArchiveLog mode. The old transaction log is not saved in NOARCHIVELOG mode. ============================================================================================================================================================================================================= = Dirty Data Block is a memory area in the computer memory, where there is a data read from the database and has modified. Dirty data block: The original data stored in the memory medium dirty data block has been modified, and the modified data has not been written in the database. Hot Data Block stores data that is frequently modified. L R u (LEAST RECENTLY Used, the Snapshot) is a read-only copy stored in one or more tables, and stores another site (remote site) from a site (primary site). The function of rollback (R O L B A c K) is to restore the data changed to the original location. Recovery Information (Undo Information) Due to various reasons, recovery information will be generated when the database needs to recover or roll back the user. ============================================================================================================================================================================================================= =
The control file is a very small file that stores some key information related to all files of the O R A C L e database. O R A C L E system Which redo logs are used when maintaining the integrity of the database (I N t e g R i t y) and determines the recovery data. ============================================================================================================================================================================================================= At least two control files per database. We have a strong recommendation that users do minimize two control files and put them on different disks, respectively. All modifications of the database structure are recorded in the control file. ============================================================================================================================================================================================================= There are two types of programs or processes. One is the user (or a client) process, such as S Q L * P L u s, Oracle Forms, Oracle Reports, and other tools for accessing the database are user processes. The server process receives a request from the customer process and then meets these requirements by interacting with the database. ================================================== Racle provides a number of support processes to help user processes communicate with database server. These support processes are used to:. Write the data file in the data file (D b W r) when the checkpoint appears. Make sure to write the dirt data block back to the disk (C K P T) when the checkpoint occurs. Read and write redo logs (L G W r). Run the function when the system is started to complete the function of the database recovery (S M O n). After the user is terminated during the session, it can be used to release the resources occupied by the user (P M o N). In A r C H i V e l O G mode, the copy (A R C H) of the redo log is filed when redo log switches. Manage the lock (L C K) in the parallel server configuration. Suspicious transactions (R E C O) are restored when using O R A C L e distributed option. . Support Oracle's snapshot technology (S NP). Supports the advanced queue of O R A C L E (q m n).
