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 segments (each with a thread), but generates much redundant data. Generally, replication 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 for data read/write, which greatly accelerates the read/write of a table. Generally, a table containing a large amount of data is defined as a hash table.

As shown in Figure 1, T1 is a replication table and T2 is a hash table.

Figure 1 Replication table and hash table