Ora-39126 Worker Unexpected Fatal Error In Kupw-worker.prepare-data-imp 71 [patched] May 2026

The error ORA-39126: Worker unexpected fatal error in KUPW$WORKER.PREPARE_DATA_IMP [71] is a generic internal error in Oracle Data Pump that typically indicates an unhandled exception within the worker process during the data import preparation phase. Root Causes

Stale or Corrupt Statistics: One of the most common triggers for ORA-39126 during the preparation or metadata loading phase is stale dictionary or fixed object statistics.

Importing System Schemas: Attempting to import internal system-related schemas (like SYSMAN, SYS, or SYSTEM) along with application schemas can lead to internal conflicts.

Data Pump Utility Corruption: The Data Pump packages or catalog objects themselves may be invalid or corrupted within the database.

Data Emoticons/Characters: Specific internal bugs (such as BUG 19712212) have linked this error to the presence of emoticons or unusual characters within table statistics that the worker fails to process.

Known Bugs: Versions such as 12.1.0.2 may be affected by BUG 28307854, specifically when importing package bodies after applying certain proactive bundle patches. Troubleshooting and Solutions

You can resolve this error by following these standard recovery steps:

Regenerate StatisticsRefreshing the dictionary and fixed object statistics often clears internal metadata mismatches: EXEC DBMS_STATS.GATHER_DICTIONARY_STATS; EXEC DBMS_STATS.GATHER_FIXED_OBJECTS_STATS;

Exclude Statistics from ImportIf the error persists during the statistics processing phase, bypass it by adding the following parameter to your impdp command: EXCLUDE=STATISTICS

You can then manually gather statistics after the data has successfully imported.

Rebuild Data Pump ComponentsIf internal packages are corrupted, you may need to reload the Data Pump utility:

For Oracle 12c and higher: Connect as SYSDBA and run @$ORACLE_HOME/rdbms/admin/dpload.sql. The error ORA-39126: Worker unexpected fatal error in

For older versions: Run @$ORACLE_HOME/rdbms/admin/catdp.sql.

Avoid SYSDBA for ImportsStandard practice is to perform imports using a user with the DATAPUMP_IMP_FULL_DATABASE role (like SYSTEM) rather than using the AS SYSDBA connection, which can cause unexpected behavior in worker processes.

Target Specific SchemasEnsure you are only importing application-specific schemas and explicitly excluding system-maintained schemas to prevent internal worker failures.

ORA-39126: Worker unexpected fatal error in KUPW$WORKER.PREPARE_DATA_IMP [71]

is a generic internal error in Oracle Data Pump that typically indicates an unhandled exception within a worker process. The specific code

often points to an issue during the initialization phase where the worker is preparing for data import. Oracle Communities Potential Causes Corrupted Data Pump Metadata

: The internal packages or views used by Data Pump may be invalid or corrupted. Missing or Incorrect Tablespaces

: If the default temporary tablespace is missing or empty, Data Pump cannot manage the metadata for the import job. Schema Conflicts : Attempting to import system schemas (like ) along with application data can trigger this fatal error. Privilege Issues : Sometimes granting IMP_FULL_DATABASE

to a non-system user can cause unexpected behavior in certain environments. Bug-related issues

: Specific versions of Oracle have known bugs (e.g., bug 28307854) that cause ORA-39126 when importing package bodies or certain metadata. Oracle Forums Common Solutions and Workarounds To resolve this error, try the following steps in order:

ORA-39126 Worker Unexpected Fatal Error in KUPW-Worker.Prepare-Data-Imp 71: Causes, Solutions, and Troubleshooting Steps Insufficient System Resources : The system may not

The ORA-39126 error is a critical issue that can occur during data import operations using Oracle Data Pump, a utility that enables you to export and import data and metadata from one database to another. This error is specifically related to the KUPW-Worker.Prepare-Data-Imp 71 process, which is a worker process responsible for preparing data for import.

Understanding the ORA-39126 Error

The ORA-39126 error message typically appears as follows:

ORA-39126: Worker unexpected fatal error in KUPW-Worker.Prepare-Data-Imp 71

This error indicates that a worker process encountered an unexpected fatal error while preparing data for import. The error can occur due to various reasons, including:

1. Insufficient System Resources: The system may not have sufficient resources, such as memory or CPU, to handle the import operation.
2. Data Corruptions: Data corruptions or inconsistencies in the export file can cause the worker process to fail.
3. Database Configuration Issues: Incorrect database configuration, such as inadequate temporary space or incorrect character set settings, can lead to the ORA-39126 error.
4. Import Parameter Settings: Incorrect import parameter settings, such as insufficient memory allocation or incorrect data type mappings, can cause the error.

Causes of the ORA-39126 Error

To troubleshoot the ORA-39126 error, it's essential to understand the underlying causes. Some common causes include:

1. Inadequate Temporary Space: Insufficient temporary space can cause the worker process to fail while preparing data for import.
2. Data Type Mismatches: Data type mismatches between the source and target databases can lead to errors during the import process.
3. Character Set Issues: Character set mismatches or incorrect character set settings can cause data corruptions or inconsistencies.
4. LOB or BFILE Data Issues: Issues with LOB (Large OBject) or BFILE (Binary File) data, such as incorrect storage or invalid data, can cause the worker process to fail.

Solutions and Troubleshooting Steps

To resolve the ORA-39126 error, follow these troubleshooting steps:

1. Check System Resources: Ensure that the system has sufficient resources, such as memory and CPU, to handle the import operation.
2. Verify Export File Integrity: Check the export file for data corruptions or inconsistencies using tools like impdp with the VERIFY option.
3. Adjust Import Parameters: Adjust import parameter settings, such as increasing memory allocation or modifying data type mappings, to ensure compatibility with the target database.
4. Increase Temporary Space: Ensure that the target database has sufficient temporary space to handle the import operation.
5. Check Character Set Settings: Verify that character set settings are correct and consistent between the source and target databases.
6. Use the SKIP_UNUSABLE_INDEXES Parameter: Set the SKIP_UNUSABLE_INDEXES parameter to Y to skip indexes that are not usable during the import process.
7. Use the SQLFILE Option: Use the SQLFILE option to generate a SQL file that can be used to recreate the import operation.

Best Practices to Avoid the ORA-39126 Error

To minimize the risk of encountering the ORA-39126 error, follow these best practices: Causes of the ORA-39126 Error To troubleshoot the

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

Conclusion

The ORA-39126 error can be a critical issue during data import operations using Oracle Data Pump. Understanding the causes, solutions, and troubleshooting steps can help database administrators and developers resolve the error efficiently. By following best practices and monitoring system resources, data integrity, and character set settings, you can minimize the risk of encountering the ORA-39126 error and ensure successful data import operations.

Solution 5: Apply Data Pump Fix Patches

Check for known bugs:

| Bug Number | Versions Affected | Description | |------------|-------------------|-------------| | 19728326 | 12.1.0.1, 12.1.0.2 | Worker fatal error with LOBs in partitioned tables | | 30578343 | 18c, 19.3-19.8 | Error 71 with XMLType or nested tables | | 35038710 | 19.9-19.14 | Corrupt worker state when importing stats | | 26257043 | 12.2, 18c | KUPW-ERROR 71 with deferred segment creation |

Apply the latest Data Pump Bundle Patch or upgrade to a stable version:

• 19.17+ (recommended)
• 21.9+

Introduction

Oracle Data Pump is a cornerstone utility for database administrators, enabling high-speed movement of data and metadata between Oracle databases. Its reliability is generally exceptional, but encountering an error such as ORA-39126: Worker unexpected fatal error in KUPW-WORKER.PREPARE-DATA-IMP (71) can be a perplexing and frustrating experience. This essay explores the nature of this error, its typical causes, and the systematic approach required to resolve it. Unlike syntax errors or permission denials, this error signals an internal inconsistency within the Data Pump worker process, demanding a deeper diagnostic strategy.

7. Insufficient Memory or PGA

The worker process requires enough Program Global Area (PGA) to prepare data, especially for large rows, LOBs, or row batches. If PGA_AGGREGATE_TARGET is too low, the worker may abort.

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3. Invalid or Missing LOB Storage

If the source uses SecureFiles LOBs and the target uses BasicFiles (or vice versa), or if the target tablespace lacks space for LOB segments, the PREPARE-DATA phase may crash.

Preventive Best Practices

To avoid this error in the future:

1. Standardize Oracle Versions – Export and import between the same patch level when possible.
2. Use VERSION parameter – On export, use VERSION=LATEST or match target version.
3. Validate before import – Use SQLFILE parameter to generate DDL and review for compatibility.
4. Monitor space and memory – Ensure target tablespaces and PGA are sized adequately.
5. Test with CONTENT=DATA_ONLY – Separate metadata and data imports to isolate issues.
6. Regularly check invalid objects – In both source and target databases.

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Diagnostic Methodology

Resolving ORA-39126 requires moving beyond a simple retry. The DBA must adopt a forensic approach:

1. Examine the Complete Log: The error message typically includes a secondary exception. Using impdp ... LOGFILE=detailed.log may reveal a ORA-31623, ORA-39125, or ORA-01403 immediately preceding the fatal error. This secondary error is the key to the root cause.
2. Identify the Culprit Table: The Data Pump log often names the table being imported when the error occurred. Isolating this table is critical.
3. Test with SQLFILE Parameter: Run the import with impdp ... SQLFILE=ddl.sql. This generates the DDL without executing it. If the DDL fails to generate or contains anomalies, the metadata is corrupted.
4. Check Versions: Compare the source and target database versions and patch levels. Mismatched versions (especially across major releases like 12.1 to 12.2) are common triggers.

Solution 3: Force ASCII mode for the dump file transfer

If the dump file was transferred via FTP:

• Re-transfer in BINARY mode (never ASCII for .dmp files)
• Verify checksums: md5sum source.dmp target.dmp