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

Direct path loads are fast but less tolerant of data anomalies. Disable it:

impdp ... ACCESS_METHOD=EXTERNAL_TABLE

Or:

impdp ... ACCESS_METHOD=SEQUENTIAL_FILE

If the import succeeds, the issue lies in direct path’s handling of your data.

The full error message usually appears as:

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

Prevention is far more efficient than cure. To minimize the risk of ORA-39126: Direct path loads are fast but less tolerant

Compare source and target table definitions (columns, data types, partitions). Use SQLFILE parameter to extract DDL from dump:

impdp ... SQLFILE=create_tables.sql

The clock on the wall read 2:14 AM. Outside the server room, the city was asleep, but inside, the air conditioning hummed a monotonous drone. Arthur, the lead DBA, was running the final migration script for the company’s new CRM system. The stakeholder meeting was at 8:00 AM, and the data pump import job was at 94%.

"Almost there," Arthur whispered, watching the terminal scroll with satisfying speed. Rows were being processed, indexes were building. He reached for his cold coffee, ready to celebrate a smooth deployment.

Then, the scrolling stopped.

It didn’t stop with a gentle "Job completed" message. It stopped with a violent, jagged block of text that turned his stomach into a knot.

ORA-39126: Worker unexpected fatal error in KUPW$WORKER.PREPARE_DATA_IMP

Arthur froze. The error code ORA-39126 was generic, a catch-all for "something terrible happened inside a Data Pump worker process." The specific location—KUPW$WORKER.PREPARE_DATA_IMP—told him the failure happened during the data preparation phase. The job wasn't just paused; it was dead.

He scrambled to check the log file, his fingers shaking slightly over the keyboard. Or: impdp

The PREPARE-DATA-IMP phase is critical because Data Pump must reconcile the source dump file’s metadata and data with the target database’s environment. Here are the most frequent triggers for this error:

When importing into a target table with a different definition than the source:

Oracle Data Pump is the backbone of modern Oracle database migrations, backups, and ETL processes. It is praised for its speed, parallelism, and fine-grained object control. However, when it fails, it often fails cryptically. Among the most dreaded errors encountered by database administrators (DBAs) is:

ORA-39126: Worker unexpected fatal error in KUPW-WORKER.PREPARE-DATA-IMP [71] If the import succeeds, the issue lies in

This error typically occurs during the import phase (impdp), specifically when the Data Pump worker process is preparing to load data into a table. The error is a "wrapper" or "umbrella" error—meaning it signals a fatal failure, but the root cause is often hidden in a secondary error stack or requires deep investigation.

In this article, we will dissect this error, explain the role of the KUPW-WORKER and the PREPARE-DATA-IMP phase, explore the most common causes (including the often-seen "71" sub-code), and provide actionable step-by-step solutions.

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