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Table Of Contents
When you must support numerous clients, and scalability is a more important factor than distribution
latency.
When the clients have a short life span. It may be desirable to keep the clients separated from the data stores
(peers or servers). If peer clients continually attach to an embedded cluster, the overhead of re-creating data
from disk or another repository becomes too expensive, and a client-server deployment should be considered
instead.
When clients reside on desktop computers or connect over a remote network. Peer connectivity between
clients may be impossible or undesirable because of rewalls and other network boundaries.
Multi-site Deployment
Both embedded peer-to-peer clusters and SQLFire server clusters are tightly-coupled by design. When members
of a SQLFire cluster must share data with each other, scalability problems are magnied if the members span
multiple networks that are spread out geographically across a WAN. To address this issue, SQLFire extends the
client-server deployment model by providing highly-available gateways that replicate data to remote clusters in
a hub-spoke model.
Understanding Multi-site Deployment on page 213
Deciding When to Use Multi-site Deployment on page 213
Understanding Multi-site Deployment
The vFabric SQLFire multi-site implementation loosely couples individual SQLFire distributed systems by using
gateways. A gateway is a logical connection between systems that replicates DML operations for congured
tables. The gateway between systems is tolerant of weak or slow physical connections between distributed system
sites. All data exchange occurs asynchronously without any loss of data or loss of event ordering.
Although the gure above shows only two SQLFire clusters joined by a gateway, you can daisy-chain multiple
distributed systems simply by adding more gateways to your deployment.
Deciding When to Use Multi-site Deployment
A wide-area network (WAN) is the main use case for the multi-site topology. The multi-site topology enables
systems at disparate geographical locations to replicate DML operations for congured tables and provide a
coherent view of the tables' data. It also ensures independence of the systems, so if any are lost from view, the
remaining systems continue to operate.
The WAN model is generally deployed either for data visibility across multiple data centers, or as a mechanism
for disaster recovery. Client applications can connect to the SQLFire cluster in the local data center, but if
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SQLFire Deployment Models