Oracle Replication Conflict Resolution

Oracle Database Tips by Donald Burleson

Oracle replication (multimaster and Streams) offers manual conflict resolution mechanisms.

Establishing conflict resolution is a process of defining rules for Oracle to apply when a conflict is detected. If the conflict is resolved, the transaction does not end up in the deferred error column group that the resolution method applies to.

You can have multiple column groups on a table and define a priority for each group. A column group can consist of all the columns in the table or any subset of those columns. Once you have created a column group, you can assign one or more conflict resolution methods to it. Oracle has defined a number of standard conflict resolution methods that will usually meet your needs. The following table provides a list of the different conflict resolution methods Oracle makes available:

METHOD NAME	DESCRIPTION
Latest Timestamp Value	With the latest timestamp value method, you define a column that contains a date data type to use in comparing multiple transactions.

Earliest Timestamp Value	This is the opposite of the above method. The method is available but rarely used.
Minimum Value, Maximum Value	When a column group has a conflict between two transactions, the minimum value method evaluates the current and new values of a defined column and selects the lower (or higher for maximum) values to determine if the new columns are applied.
Group Priority Value	In this case, column groups are assigned a priority and conflicts are adjudicated to the highest priority group.
Site Priority Value	In this instance, sites are assigned a priority. When two transactions conflict, the transaction from the master site with the highest priority will be applied. This is actually a special case of the Group Priority Value method above.

Conflict Resolution never performs a rollback of a transaction. Since all master sites will contain the same resolution methods, each site should apply the same transactions. If transaction A overwrites transaction B, the site that originally creates transaction B will eventually overwrite it with transaction A.

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