Database
Databases manage various data objects and are isolated from each other. While creating a database, you can specify a tablespace. If you do not specify it, the object will be saved to the PG_DEFAULT tablespace by default. Objects managed by a database can be distributed to multiple tablespaces.
Tablespace
In openGauss, a tablespace is a directory storing physical files of the databases the tablespace contains. Multiple tablespaces can coexist. Files are physically isolated using tablespaces and managed by a file system.
Schema
openGauss schemas logically separate databases. All database objects are created under certain schemas. In openGauss, schemas and users are loosely bound. When you create a user, a schema with the same name as the user will be created automatically. You can also create a schema or specify another schema.
User and Role
openGauss uses users and roles to control the access to databases. A role can be a database user or a group of database users, depending on role settings. In openGauss, the difference between roles and users is that a role does not have the LOGIN permission by default. In openGauss, one user can have only one role, but you can put a user's role under a parent role to grant multiple permissions to the user.
Transaction
In openGauss, transactions are managed by multi-version concurrency control (MVCC) and two-phase locking (2PL). It enables smooth data reads and writes. openGauss stores them together with the version of the current tuple. A VACUUM thread is introduced to periodically clear historical version data. Unless in performance optimization, you do not need to pay attention to the VACUUM process. In addition, openGauss automatically commits transactions.
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