Defining Master Replicates

To guarantee consistency between the nodes in your Enterprise Replication environment, you can define master replicates using the cdr define replicate command with the --master option. Dictionary information is then stored about replicated column attributes for the participant you specify. This enables Enterprise Replication to check for consistency between this master definition and local participant definitions. Checks are performed when the replicate is defined and each time a new participant is added to the replicate, thus avoiding runtime errors. Verification also occurs each time the master replicate is started on a server.

Defining a replicate as a master replicate provides several advantages:

• Ensures data integrity by verifying that all participants in the replicate have table and replicated column attributes that match the master replicate definition.
• Provides automatic table generation on participants that do not already contain the table specified in the master replicate. However, Enterprise Replication cannot create tables with user-defined data types.
• Allows alter operations on the replicated tables. For more information, see Performing Alter Operations on Replicated Tables.

When you define a master replicate, you must specify a participant that is on the server for which you are running the command. This participant is used to create the dictionary information for the master replicate. If you specify additional participants in the cdr define replicate command, they are verified against the master definition and added to the replicate if they pass validation. If any participant fails validation, the cdr define replicate command fails and that participant is disabled.

The master replicate options, described in subsections below, are:

• --name

  Use this option to create a strict master replicate that supports alter operations and remastering.

• --empty

  Use this option to create an empty master replicate and add participants later.

Master Replicate Verification

Enterprise Replication verifies the following information about a participant when the participant is added to the master replicate:

• The participant contains all replicated columns.
• The replicated columns in the participant have the correct data types. For columns that are user-defined data types, only the names of the data types are verified.
• Optionally, the replicated columns in the participant have the same column names as the master replicate.

Creating Strict Master Replicates

You can create a strict master replicate in which all participants have the same replicated column names by using the --name=y option. This option specifies that when the master replicate verification is done for a new participant, that the column names on the participant must be identical to the column names of the master replicate. Strict master replicates allow you to perform the following tasks:

• Alter operations on replicated tables. For more information, see Performing Alter Operations on Replicated Tables.
• Remastering by using the cdr remaster command. For more information, see Remastering a Replicate.

You can modify an existing master replicate to remove name verification by using the --name=n option of the cdr modify replicate command.

Creating Empty Master Replicates

You can create an empty master replicate by using the --empty option. This option allows you to specify a participant as the basis of the master replicate but not include that participant in the replicate. Creating an empty replicate can be convenient in large environments in which you later add all participants using scripts.

When you define an empty master replicate, you must specify only one participant in the cdr define replicate command. This participant is used to create the master dictionary information but is not added to the replicate.

The --empty option is only supported for master replicates, you cannot use it without the --master option.