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Logical storage structure is the division of data storage structure in logical concept. The logical storage structure of oracle is mainly composed of the concepts of table space, segment, interval and data block. Oracle data block is composed of multiple tablespaces, tablespaces are composed of multiple segments, segments are composed of multiple data areas, and data areas are composed of multiple blocks. Data block is not only the smallest logical unit in Oracle logical storage, but also the smallest storage unit for data input and output. The data block consists of block headers, table catalogs, row directories, free space, and row data. The combination of block, table directory and row directory is called the header information area. the header information area does not store data and stores the guide information of the whole block, which plays the role of guiding the system to read the data. A storage area in which free space and row data are shared as blocks for storing real data records.

The data area is the smallest unit of Oracle storage allocation, and oracle extends the storage control based on the data area. The purpose of using the data area is to hold data of a specific data type, and is also the basic unit of data growth in the table. In an Oracle database, storage space is allocated on a data area basis.

A segment consists of one or more data areas and is an independent logical storage structure for storing space-consuming data objects such as tables, indexes, or clusters. A segment belongs to only a specific data object, and whenever a data object with a separate segment is created, Oracle creates a segment for it. An Oracle database usually has four types of segments. (1) data segment (2) index segment (3) rollback segment (4) temporary segment

A tablespace is the maximum logically partitioned area of a database, and any data object must be specified to be stored in a tablespace at the time of creation. Tablespaces (belonging to logical storage structure) correspond to data files (belonging to physical storage structure). A tablespace consists of one or more data files, and a data file belongs to only one tablespace. The storage space of Oracle data is represented as tablespaces logically and physically as data files.

When creating a database, the Oracle system automatically creates multiple default tablespaces. These tablespaces are not only used to manage user data tablespaces, but also include tablespaces for managing Oracle system internal data (such as data dictionaries), Oracle 11g default creation of bar main tablespaces (1) SYSTEM tablespaces, system tablespaces (2) SYSAUX tablespaces, SYSTEM auxiliary tablespaces (3) UNDO tablespaces. Undo tablespace, the tablespace used to store undo messages. (4) USERS tablespace. User tablespace, the tablespace Oracle recommends users to use. Various data objects can be created on this tablespace. The sample user of the Oracle system, the SCOTT object, is stored in the USERS table space. In addition to the tablespaces created by default in the Oracle system, users can create multiple custom tablespaces according to the actual situation of the application system and the types of objects to be stored, so as to distinguish user data from system data. In addition, the data of different application systems should be stored on different table spaces, and the files of different table spaces should be stored on different disks, so as to reduce the conflict between I and O and improve the operation performance of the application system.

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