Selecting a Distribution Mode

In replication mode, full data in a table is copied to each DN in the cluster. This mode is used for tables containing a small volume of data. Full data in a table stored on each DN avoids data redistribution during the join operation. This reduces network costs and plan segment (each having a thread), but generates much redundant data. Generally, this mode is only used for small dimension tables.

In hash mode, hash values are generated for one or more columns. You can obtain the storage location of a tuple based on the mapping between DNs and the hash values. In a hash table, I/O resources on each node can be used during data read/write, which improves the read/write speed of a table. Generally, a table containing a large amount data is defined as a hash table.

Range distribution and list distribution are user-defined distribution policies. Values in a distribution column are within a certain range or fall into a specific value range of the corresponding target DN. The two distribution modes facilitate flexible data management which, however, requires users equipped with certain data abstraction capability.

Policy	Description	Application Scenario
Hash	Table data is distributed on all DNs in the cluster.	Fact tables containing a large amount of data
Replication	Full data in a table is stored on every DN in the cluster.	Small tables and dimension tables
Range	Table data is mapped to specified columns based on the range and distributed to the corresponding DNs.	Users need to customize distribution rules.
List	Table data is mapped to specified columns based on specific values and distributed to corresponding DNs.	Users need to customize distribution rules.