Pre-built update conflict handlers
The DISCARD handler behaves differently.
When conflict arises, it ignores the source database values. As
a result, in the above example, the value of 62000 at the London
site will remain.
When the MAXIMUM handler is used, the new
value and the old values are compared and the higher values is
retained or applied. In the above example, 62000 would be
retained since it is higher than 45000. In the same way, if the
MINIMUM conflict handler had been used, the value of 45000 would
have been applied.
Conclusion
In this chapter, the focus has been on the
principle components of the Streams process that are relevant
for the replication process. The main points of this chapter
include:
-
The Capture processes can be configured on
the source database where transactions are effected as well as
on an intermediate database which is known as the Down Streams
capture database.
-
Object instantiation methods and
supplemental logging methods are essential for data replication.
Instantiation prepares the objects for replication. Supplemental
logging adds extra data values to the redo entries.
-
Session Tags help to develop better control
over what can be replicated and what can not. Administrators can
use the tags to solve data mismatch issues, etc.
-
In multi-way replication, conflicts do
arise. There are specific design considerations that can be used
to resolve them. There are also Oracle provided pre-built
conflict update handlers that can be used help to resolve
conflicts.
In the next chapter, the configuration
details of the two main Streams clients will be presented.
These two main clients are the Capture process and the
Propagation process.
