This chapter contains guidelines for preparing the database and the system to support Oracle GoldenGate. This chapter contains the following sections:
The following table attributes must be addressed in an Oracle GoldenGate environment.
Section 3.1.1, "Disabling Triggers and Cascade Constraints"
Section 3.1.2, "Assigning Row Identifiers"
Disable triggers, cascade delete constraints, and cascade update constraints on target Teradata tables. Oracle GoldenGate replicates DML that results from a trigger or cascade constraint. If the same trigger or constraint gets activated on the target table, it becomes redundant because of the replicated version, and the database returns an error. Consider the following example, where the source tables are emp_src and salary_src and the target tables are emp_targ and salary_targ.
A delete is issued for emp_src.
It cascades a delete to salary_src.
Oracle GoldenGate sends both deletes to the target.
The parent delete arrives first and is applied to emp_targ.
The parent delete cascades a delete to salary_targ.
The cascaded delete from salary_src is applied to salary_targ.
The row cannot be located because it was already deleted in step 5.
Oracle GoldenGate requires some form of unique row identifier on the source and target tables to locate the correct target rows for replicated updates and deletes.
Unless a KEYCOLS clause is used in the TABLE or MAP statement, Oracle GoldenGate selects a row identifier to use in the following order of priority:
Primary key
First unique key alphanumerically that does not contain a timestamp or non-materialized computed column.
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 are not supported by Oracle GoldenGate 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 if there are no keys at all 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 larger, less efficientWHERE clause.If a table does not have one of the preceding types of row identifiers, or if you prefer those identifiers not to be 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 Replicat MAP parameter. The specified key will override any existing primary or unique key that Oracle GoldenGate finds. For more information, see Reference for Oracle GoldenGate for Windows and UNIX.