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RTR Terminology
Figure 1–12 Standby Server Configuration
LKG-11210-98WI
TR
BE
DB
BE
Server
Server
Primary
Server
Standby
Server
Transactional
shadowing
To increase transaction availability, transactions can be
shadowed with a shadow server. This is called transactional
shadowing and is accomplished by having a second location,
often at a different site, where transactions are also recorded.
This is illustrated in Figure 1–13. Data are recorded in two
separate data stores or databases. The router knows about both
backends and sends all transactions to both backends. RTR
provides the server application with the necessary information to
keep the two databases synchronized.
RTR Journal
In the RTR environment, one data store (database or data
file) is elected the primary, and a second data store is made
the shadow. The shadow data store is a copy of the data store
kept on the primary. If either data store becomes unavailable,
all transactions continue to be processed and stored on the
surviving data store. At the same time, RTR makes a record
of (remembers) all transactions stored only on the shadow data
store in the RTR journal by the shadow server. When the
primary server and data store become available again, RTR
replays the transactions in the journal to the primary data store
through the primary server. This brings the data store back into
synchronization.
Introduction 1–13