Database Logical Architecture

Each DN in a cluster stores data on disks. This section describes the objects on each DN from the logical view, the relationship between these objects, and how data is distributed on different nodes. Figure 1 shows the database logical structure.

Figure 1 Database logical architecture

• A tablespace is a directory. A database contains one or more tablespaces to store physical files of the database. Each tablespace can contain files belonging to different databases.
• A database manages various data objects and is isolated from each other. Objects managed by a database can be distributed to multiple tablespaces.
• A datafile segment stores data of only one table. A table containing more than 1 GB of data is stored in multiple datafile segments.
• One table belongs to only one database and one tablespace. The datafile segments storing the data of the same table must be in the same tablespace.
• A block is a basic unit for database management. Its default size is 8 KB.
• Data can be distributed on DNs in replication, hash, range, or list mode. You can specify a mode when creating a table.