Synchronization=keyword
Specifies the degree to which you want to synchronize committed
transactions on the standby database with committed transactions
on the master database.
Applicable to: Master database
Required or Optional: Optional
Default Value: Synchronization=Cold
When you enable replication operations, server processes on the
master database write transactions to the after-image journal
for the master database and send them across the network to
the after-image journal for the standby database. The standby
database acknowledges the receipt of the transactional message
and handles after-image journaling depending on the mode you have
set with the Synchronization qualifier.
Table 28 Keywords for the Synchronization Qualifier
Performance
Impact
Equivalence on
of Committed Master Standby Database
Keyword Transactions Database Recoverability
Commit When the standby Highest The standby database is
database transactionally identical
receives the and recoverable with respect
AIJ information to the master database.
from the master
database, the
servers on the
standby database:
1. Write it to
the after-
image journal
on the standby
system
2. Apply the AIJ
to the standby
database
3. Send a message
back to
the master
database
acknowledging
the successful
commit of the
transaction
Hot When the standby High The standby database is
database extremely close to being
receives the transactionally identical to
AIJ information the master database.
from the master
database, the After-image journal records
servers on the in transit are received
standby database: and committed. Some restart
processing may be required
1. Write it to to synchronize the database.
the AIJ on the
standby system
2. Send a message
back to
the master
database
before
applying the
transaction
to the standby
database
Warm When the standby Medium The standby database is
database transactionally close to
receives the the master database, but the
AIJ information databases are not identical.
from the master
database, the There may be transactions
servers on the rolled back on the standby
standby database: database that have been
committed on the master
o Send a message database.
back to
the master
database
before
applying the
transaction to
either the AIJ
or the standby
database
o Might not
commit after-
image journal
records to the
database
Cold When the standby Low The standby database is
(de- database not immediately recoverable
fault) receives the transactionally with respect
AIJ information to the master database.
from the master
database: After-image journal records
in transit could be lost.
o The servers
never return
a message
acknowledging
the receipt
of the AIJ
information
o In failover
situations,
it is
possible that
transactions
rolled back
on the standby
database were
committed on
the master
database
For each level of database synchronization, you make a trade-off
between how closely the standby and master databases match each
other in regard to committed transactions against performance.
For example, the Synchronization=Cold level provides the fastest
performance for the master database, but the lowest level of
master and standby database synchronization. However, in some
business environments, this trade-off might be acceptable. In
such an environment, the speed of master database performance
outweighs the risk of losing recent transactions in the event of
failover; system throughput has greater financial importance and
impact than the value of individual aij records (transactions).
Recommendation: For high-performance applications, Oracle
Corporation recommends that you do not specify both the
Synchronization=Cold and the Governor=Disabled qualifiers when
you start replication on the standby system. This is because
the master database can possibly outperform the standby database
during updates. The replication governor should be enabled to
prevent the master and standby databases from getting too far out
of synchronization.
NOTE
You can define logical names to specify the synchronization
mode, or to enable or disable the replication governor.