Automatic Conflict Detection and Resolution

You can configure automatic conflict detection and resolution in an Oracle GoldenGate configuration that replicates tables between Oracle databases. To configure automatic conflict detection and resolution for a table, you need to call the ADD_AUTO_CDR procedure in the DBMS_GOLDENGATE_ADM package. A prerequisite for setting up automatic conflict detection and resolution, the Oracle GoldenGate user must have the appropriate privileges. See Grant User Privileges for Oracle Database for Oracle GoldenGate Classic Architecture learn about user privileges.

The administrator user must be logged in to the appropriate PDB when calling the ADD_AUTO_CDR. The following constants, which represent bit flags are now added:

EARLIEST_TIMESTAMP_RESOLUTION sets TOMBSTONE KEY VERSIONING automatically
DELETE_ALWAYS_WINS sets TOMBSTONE KEY VERSIONING automatically.
IGNORE_SITE_PRIORITY

The following example uses an ALTER command for the HR.EMPLOYEES table:

BEGIN
 dbms_goldengate_adm.alter_auto_cdr
 (schema_name => 'HR' 
 ,table_name => 'EMPLOYEES' 
 ,additional_options => DBMS_GOLDENGATE_ADM.ADDITIONAL_OPTIONS_ADD_KEY_VERSION );
END;
/

See the description for additional_options in ADD_AUTO_CDR Procedure of Oracle Database PL/SQL Packages and Types Reference.

When Oracle GoldenGate captures changes that originated at an Oracle Database, each change is encapsulated in a row logical change record (LCR). A row LCR is a structured representation of a DML row change. Each row LCR includes the operation type, old column values, and new column values. Multiple row LCRs can be part of a single database transaction.

When more than one replica of a table allows changes to the table, a conflict can occur when a change is made to the same row in two different databases at nearly the same time. Oracle GoldenGate replicates changes using the row LCRs. It detects a conflict by comparing the old values in the row LCR for the initial change from the origin database with the current values of the corresponding table row at the destination database identified by the key columns. If any column value does not match, then there is a conflict.

After a conflict is detected, Oracle GoldenGate can resolve the conflict by overwriting values in the row with some values from the row LCR, ignoring the values in the row LCR, or computing a delta to update the row values.

Automatic conflict detection and resolution does not require application changes for the following reasons:

Oracle Database automatically creates and maintains invisible timestamp columns.
Inserts, updates, and deletes use the delete tombstone log table to determine if a row was deleted.
LOB column conflicts can be detected.
Oracle Database automatically configures supplemental logging on required columns.