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How the connection is secured (SSL, client authentication, or no SSL).
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Any attributes that will not be replicated (see "Fractional Replication," on
page 127).
Data Consistency
Consistency refers to how closely the contents of replicated databases match each
other at a given point in time. When you set up replication between two servers,
part of the configuration is to schedule updates. The supplier server always
determines when consumer servers need to be updated and initiates replication.
Directory Server offers the option of keeping replicas always synchronized or of
scheduling updates for a particular time of day or day in the week. The advantage
of keeping replicas always in sync is obviously that it provides better data
consistency. The cost is the network traffic resulting from the frequent update
operations. This solution is the best in cases where:
•
You have a reliable high-speed connection between servers.
•
The client requests serviced by your directory are mainly search, read, and
compare operations, with relatively few update operations.
In cases where you can afford to have looser consistency in data, you can choose
the frequency of updates that best suits your needs or lowers the affect on network
traffic. This solution is the best in cases where:
•
You have unreliable or intermittently available network connections (such as a
dial-up connection to synchronize replicas).
•
The client requests serviced by your directory are mainly update operations.
•
You need to reduce the communication costs.
In the case of multi-master replication, the replicas on each supplier are said to be
loosely consistent because at any given time, there can be differences in the data
stored on each supplier. This is true, even when you have selected to always keep
replicas in sync, for two reasons:
•
There is a latency in the propagation of update operations between suppliers.
•
The supplier that serviced the update operation does not wait for the second
supplier to validate it before returning an "operation successful" message to
the client.
Introduction to Replication
Chapter 6
Designing the Replication Process
115
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