User guide

Replication
Replication is a task that synchronizes the hub and spoke server databases. By default,
replication runs every 12 hours on each spoke server. A spoke server’s first replication occurs
automatically when the spoke server is added to the DSView software system. You may change
the interval that the replication task runs on each spoke server, or you may initiate an
immediate replication.
During replication, the spoke server sends all of its database changes since the last replication
to the hub server. The hub server then incorporates those changes and sends all of its database
changes since the last replication to the spoke server (excluding the changes that spoke server
just sent to the hub server).
If an item is added on a spoke server, and another item with the same name (but perhaps with
different configuration parameters) is added on the hub server, then after replication, both items
will appear on both the hub and spoke servers, with a tilde (~) and a number added to one of
the names. The administrator should handle the issue appropriately - in some cases, the
duplicate item may need to be renamed; in others, the duplicate item should be deleted.
When different changes are made to one existing item, two outcomes are possible. For example,
assume an item is added and configured on the hub server and is then replicated to the spoke
server. Later, an administrator changes something about the item on the spoke server. Another
administrator then changes something about the item on the hub server. When the replication
task runs, two things may happen.
In a few instances where no conflict occurs, both changes will be incorporated and replicated.
For example, if the hub server’s administrator adds username JaneDoe to the existing user-
defined user group Accounting and the spoke server’s administrator adds username JohnDoe to
the Accounting user group, both names will be added and replicated.
In most other instances where the changes are mutually exclusive or some other conflict occurs,
the most recent change will be the only change accepted and replicated. For example, if the
hub server’s administrator associates a unit with the Miami site, and the spoke server’s
administrator associates the same unit with the Chicago site, the change that was made closest
to the time of replication (that is, the most recent change) will be accepted and replicated.
This emphasizes the importance of ensuring the hub and spoke servers’ clocks are synchronized.
The exception to the last-change rule is when one of the actions deletes an item - in that case,
the deletion is accepted and replicated, regardless of timing. For example, if a unit was deleted
on the hub server, and then the contact information for the same unit was changed on the spoke
server a minute later, the unit will be deleted when the replication task is run.
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