Projection Replication

Replication consists of creating duplicates of unsegmented superprojections on multiple nodes (typically all nodes in a database). Replication has two purposes:

• distributed query execution
• K-Safety (a pair of replicated superprojections can be used as buddy projections for the purpose of recovery)

  Buddy projections are required for K-Safety. Two projections are considered to be buddies if they contain the same columns and have the same range segmentation or hash segmentation using different node ordering. Buddy projections usually have different sort orders for query performance purposes.

  K represents the maximum number of nodes in a database that can fail and recover with no loss of data. In Vertica V2.1, the value of K can be zero (0) or one (1). The value of K can be one (1) only when the Physical Schema design meets certain requirements. The designs generated by the Database Designer are K-Safe.

  A physical schema consists of a set of projections used to store data on disk. The projections in the physical schema are based on the objects in the Logical Schema.

Vertica provides SQL syntax that automatically replicates an unsegmented superprojection across all nodes in a database (or specific nodes). Automatic replication is used by the Database Designer and is the preferred method of creating custom replicated projections.