Oracle GoldenGate requires a unique row identifier on the source and target tables to locate the correct target rows for replicated updates and deletes.

Unless a KEYCOLS clause exists in the TABLE or MAP statement, Oracle GoldenGate selects a row identifier to use in the following order of priority:

1. Primary key

2. First unique key alphanumerically that does not contain a timestamp or non-materialized computed column.

3. If none of the preceding key types exist (even though there might be other types of keys defined on the table) Oracle GoldenGate constructs a pseudo key of all columns that the database allows to be used in a unique key, excluding those that Oracle GoldenGate does not supported in a key or those that are excluded from the Oracle GoldenGate configuration.

   Note:

   If there are other non-usable keys on a table or no keys on the table, Oracle GoldenGate logs an appropriate message to the report file. Constructing a key from all of the columns impedes the performance of Oracle GoldenGate on the source system. On the target, this key causes Replicat to use a more extensive, less efficient WHERE clause.

4. If a table does not have an appropriate key, or if you prefer that the existing key(s) are not used, you can define a substitute key, if the table has columns that always contain unique values. You define this substitute key by including a KEYCOLS clause within the Extract TABLE and the Replicat MAP parameters. The specified key will override any existing primary or unique key that Oracle GoldenGate finds. See TABLE | MAP in Reference for Oracle GoldenGate.