Data Redundancy Solutions | 287
Site and network stability
If a site or a network goes down, all replications that use that network or are destined
for that site will not be received. When either of these resources comes
back online, the stored replication traffic can have an impact on the amount of
time it takes to recover the site.
Experience level of your database administrators
Even the most effective replication plan can be undone by DBAs who aren??™t
familiar with replication.
Figure 11-11 illustrates synchronous and asynchronous replication.
Synchronous, or real-time, replication can be used when there is no tolerance for
data divergence or lost data. The data at the secondary site must match the primary
site at all times and reflect all committed transactions. Each transaction at the primary
site will fire triggers that call procedures at the secondary site to reproduce the
transaction. Synchronous replication uses distributed transactions that will add
overhead to every transaction at the primary site. Whether this additional overhead is
acceptable will clearly depend on your specific requirements.
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