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Some database management systems allow tablespaces to be configured directly over operating-system device entries, called raw devices, providing better performance by avoiding the OS filesystem overheads. Oracle stores data logically in tablespaces and physically in datafiles associated with the corresponding tablespace.
However, Oracle databases store schema objects logically within a tablespace of the database. The data of each object is physically contained in one or more of the tablespace's datafiles . For some objects (such as tables, indexes, and clusters) a database administrator can specify how much disk space the Oracle RDBMS allocates for the object ...
Whenever something changes in a datafile, Oracle records the change in the redo log. The name redo log indicates its purpose: If the database crashes, the RDBMS can redo (re-process) all changes on datafiles which will take the database data back to the state it was when the last redo record was written.
Oracle acquired Innobase, supplier of the InnoDB codebase to MySQL, in part to compete better against open source alternatives, and acquired Sun Microsystems, owner of MySQL, in 2010. Database products licensed as open-source are, by the legal terms of the Open Source Definition , free to distribute and free of royalty or other licensing fees.
Note (2): MariaDB and MySQL provide ACID compliance through the default InnoDB storage engine. [71] [72] Note (3): "For other than InnoDB storage engines, MySQL Server parses and ignores the FOREIGN KEY and REFERENCES syntax in CREATE TABLE statements. The CHECK clause is parsed but ignored by all storage engines." [73]
Oracle Database provides information about all of the tables, views, columns, and procedures in a database. This information about information is known as metadata. [1] It is stored in two locations: data dictionary tables (accessed via built-in views) and a metadata registry.
Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. In a non-RAC Oracle database, a single instance accesses a single database. The database consists of a collection of data files, control files, and redo logs located on disk.
SQLite: A VIEW named "dual" that works the same as the Oracle "dual" table can be created as follows: CREATE VIEW dual AS SELECT 'x' AS dummy; SAP HANA has a table called DUMMY that works the same as the Oracle "dual" table. Teradata database does not require a dummy table. Queries like 'select 1 + 1' can be run without a "from" clause/table name.