Ora-39126 Worker Unexpected Fatal: Error In Kupw-worker.prepare-data-imp 71

The error ORA-39126: Worker unexpected fatal error in KUPW$WORKER.PREPARE_DATA_IMP [71] is a generic internal failure within the Oracle Data Pump import process. It typically indicates that the worker process encountered an unhandled exception while preparing for a data import, often triggered by inconsistent metadata, corrupt dictionary statistics, or invalid internal packages. Potential Causes

Prevention

Always transfer .dmp files in binary mode
Ensure NLS_LANG matches between source and target
Use the same Oracle version (or newer target, but not older) for export/import
Validate dump files with impdp ... validate=full before production import
Set FILESIZE to split large dumps rather than creating multi-gigabyte single files

Test Export and Import Operations: Test export and import operations in a non-production environment to ensure compatibility and identify potential issues.
Monitor System Resources: Monitor system resources during import operations to ensure sufficient resources are available.
Use Compatible Character Sets: Use compatible character sets between the source and target databases.
Verify Data Integrity: Verify data integrity before and after import operations using tools like DBVERIFY or impdp with the VERIFY option.
Regularly Maintain Database Statistics: Regularly maintain database statistics to ensure accurate data distribution and prevent data skew.

ORA-39126: Worker unexpected fatal error in KUPW-WORKER.PREPARE-DATA-IMP 
[worker_process_id] 
ORA-XXXXX: Underlying cause

VARCHAR2 to CLOB conversion issues
DATE vs TIMESTAMP mismatches
Character set conversion failures (e.g., AL32UTF8 to WE8MSWIN1252)
Invalid values for NUMBER or INTERVAL columns

ORA-02374 – conversion error
ORA-12899 – value too large for column
ORA-01461 – can bind LONG value only for insert into LONG column
ORA-06502 – PL/SQL numeric or value error

6. Apply latest Oracle patches

Check My Oracle Support for bug fixes related to ORA-39126 and KUPW-WORKER.PREPARE-DATA-IMP. Common patches: The error ORA-39126: Worker unexpected fatal error in

Note: In a Multitenant environment, ensure all PDBs are open and run this from the CDB. 2. Refresh Dictionary Statistics Always transfer

The most frequent cause of error [71] is a failure in processing table statistics. You can bypass this by excluding statistics during the import and gathering them manually later. Add this parameter to your impdp command: EXCLUDE=STATISTICS Use code with caution. Test Export and Import Operations : Test export