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Table Of Contents
An example sequence of event routing:
1. A congured table in Site 1 is updated.
2. Site 1 distributes a DML event to both Site 2 and Site 3. The DML event lists Site 1 as the originator, and
sites 2 and 3 as the destinations.
3. Site 2 receives and applies the DML event. Although Site 2 is congured to replicate table DML operations
to Site 3, the DML event indicates that Site 3 is already a destination for the DML operation, so it does not
forward the event to Site 3.
4. Site 3 receives and applies the DML event. Although Site 3 is congured to replicate table DML operations
to Site 2, the DML event indicates that Site 2 is already a destination for the DML operation, so it does not
forward the event to Site 2.
In other words the parallel topology ensures that under normal operating conditions, a DML operation at any
one site is applied once and only once to every other connected site in the WAN.
Unsupported Topologies
Any topology in which one or more of the congured WAN sites does not contain a gateway to every other
WAN site can lead to a variety of problems, and is unsupported. The most signicant problem occurs when sites
are congured so that one or more sites receive multiple copies of the same DML event.
For example, in the following unsupported conguration causes site 4 to apply the same DML event multiple
times.
The sequence of event routing is:
1. A congured table in Site 1 is updated.
2. Site 1 distributes a DML event to both Site 2 and Site 3. The DML event lists Site 1 as the originator, and
sites 2 and 3 as the destinations.
3. Site 2 receives and applies the DML event. However, it is congured to distribute DML operations for the
table to Site 4. Because the DML event from Site 1 does not list Site 4 as a destination, it forwards the event
to Site 4. The DML event lists Site 2 as the originator and Site 4 as the destination.
4. Site 3 receives and applies the DML event. However, it is also congured to distribute DML operations for
the table to Site 4. Because the DML event from Site 1 does not list Site 4 as a destination, it also forwards
the event to Site 4. The DML event lists Site 3 as the originator and Site 4 as the destination.
5. Site 4 receives the DML events sent from Sites 2 and 3. Because each event has a unique originator, there is
no way to determine that both events originated from the single DML operation in Site 1. Site 4 applies both
DML events, and the table now contains inconsistent data in Site 4.
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