Enterprise Replication Terminology

Enterprise Replication server

An Enterprise Replication server, or replication server, is the HCL® OneDB® database server that participates in data replication.

The replication server maintains information about the replication environment, which columns are replicated, and the conditions under which the data is replicated. This information is stored in a database, syscdr, that the database server creates when it is initialized. Multiple database servers can be on the same physical computer, and each database server can participate in Enterprise Replication.

Shard server

A shard server is a database server that participates in data replication and receives horizontally partitioned (sharded) data. A shard cluster is the group of database servers over which a table or collection is partitioned.

Replication key

A replication key consists of one or more columns that uniquely identifies each replicated row. The replication key must be the same on all servers that participate in the replicate. Typically, the replication key is a primary key constraint. Otherwise, you can specify ERKEY shadow columns or another unique index as the replication key.

The replication key for a shard cluster consists of a single column, and is called a shard key.

Replicate

A replicate defines the replication participants and various attributes of how to replicate the data, such as frequency and how to handle any conflicts during replication.

For more information, see Define a replicate and cdr define replicate.

Master replicate

A master replicate is a replicate that guarantees data integrity by verifying that replicated tables on different servers have consistent column attributes. Master replicates also support alter operations on replicated tables.

Shadow replicate

A shadow replicate is a copy of an existing (primary) replicate. Shadow replicates allow Enterprise Replication to manage alter and repair operations on replicated tables.

Participant

A participant specifies the data (database, table, and columns) to replicate and the database servers to which the data replicates.

Replicate set

A replicate set combines several replicates to form a set that can be administered together as a unit.

Template

A template provides a mechanism to set up and deploy replication for a group of tables on one or more servers. A template is especially useful if you have many tables to replicate between many servers. A template defines a group of master replicates and a replicate set for a specified group of tables that are based on attributes such as database, tables, columns, and primary keys from the master node.

You create a template by running the cdr define template command and then instantiate, or realize, it on servers with the cdr realize template command.

Global catalog

Each database server that participates in Enterprise Replication maintains tables in the syscdr database to track Enterprise Replication configuration information and state. For all root and nonroot replication servers, this catalog is a global catalog that maintains a global inventory of Enterprise Replication configuration information. The global catalog is created when you define the server for replication.

Grid

A grid is a set of replication servers that you can administer as a unit. When you run SQL data definition statements from within a grid context on one server in the grid, they are propagated to all other servers in the grid. You can run SQL data manipulation statements and routines through grid routines. You can propagate external files to other servers in the grid. You can run grid queries to consolidate data from multiple grid servers.