Why Is Error ORA-01555 Reported During Migration from Oracle to DWS?

Symptom

When CDM is used to migrate Oracle data to DWS, an error is reported, as shown in Figure 1.

Figure 1 Symptom

Cause Analysis

1. During data migration, if the entire table is queried and the table contains a large amount of data, the query takes a long time.
2. During the query, other users frequently perform the commit operation.
3. The RBS (the tablespace used for rollback) of Oracle is small. As a result, the migration task is not complete, the source database has been updated, and the rollback times out.

Summary and Suggestions

1. Reduce the data volume queried each time.
2. Modify the database configurations to increase the RBS of the Oracle database.