Synchronous replication
introduces system interdependencies??”the secondary site and the network connecting
the sites must be up or the primary site will not be able to perform transactions.
You can also use asynchronous, or deferred, replication to provide redundant data.
With asynchronous replication, transactions are performed at the primary site and
replicated some time later to the secondary site. Until the deferred transaction queue
is ???pushed??? to the secondary site, replicating the changes, the data at the secondary
Figure 11-11. Oracle replication for redundant data
TABLE X
Secondary Database
TABLE X
Deferred
Transaction Queue
Place in Queue
TABLE X
Secondary Database
Asynchronous Transaction
TIME
Primary Database
Transaction
TABLE X
Primary Database
Synchronous
1 2
Replication
4 3
1 2
4 3
Replication
288 | Chapter 11: Oracle and High Availability
site will differ from the primary site data. If the primary database is irrevocably lost,
any unpushed transactions in the deferred queue will also be lost.
Pages:
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629