Introduction to Oracle:
Oracle Database, also known as Oracle RDBMS, or Oracle for short. It is a relational database management system from Oracle Corporation.
The biggest difference between a SQL Server database and an Oracle database is the tablespace design. Oracle database pioneered the design concept of table space, which made an indelible contribution to the high performance of Oracle database. It can be said that many optimizations in Oracle are based on the design concept of table space.
The ORACLE database is divided into logical areas called tablespaces - forming the logical structure of the ORACLE database. An ORACLE database can have one or more table spaces, and a table space corresponds to one or more physical database files. Table space is the smallest unit of ORACLE database recovery, which holds many database entities, such as tables, views, indexes, clusters, rollback segments and temporary segments.
We can create different table spaces in the Oracle database, set the maximum storage capacity for them, and then assign users to this table space. In this case, the storage capacity of the user is limited by the size of the table space.
Logical structure:
The logical structure of Oracle consists of at least one tablespace and database schema objects. Here a schema is a collection of objects, and a schema object is a logical structure that directly references database data. Schema objects include structures such as tables, views, sequences, stored procedures, synonyms, indexes, clusters, and database chains. Logical storage structures, including tablespaces, segments, and ranges, describe how the database's physical space is used.
In summary, the logical structure consists of logical storage structures (tablespaces, segments, ranges, blocks) and logical data structures (tables, views, sequences, stored procedures, synonyms, indexes, clusters and database chains, etc.), and the schema objects ( logical data structures) and relationships form the relational design of the database.
Segment (Segment): It is a logical storage structure of a specified type in the table space, which consists of one or more ranges, and the segment will occupy and grow the storage space. These include: data segment (used to store table data), index segment (used to store table index), temporary segment (used to store intermediate results), rollback segment (used to restore transactions in the event of an exception)
Extent: It is the logical unit of database storage space allocation. A range is composed of many consecutive data blocks. The range is allocated by segments. The first range allocated is called the initial range, and the range allocated later is called the incremental range. amount range.
Data block (Block): It is the smallest unit of IO operation in the database. It is not the same concept as the block of the operating system. Oracle database does not request data in units of operating system blocks, but in units of multiple Oracle database blocks.