AWS DMS CDC Converter Error from Postgres 18 to Oracle 19

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If you’re experiencing issues with AWS Database Migration Service (DMS) when migrating data from PostgreSQL to Oracle, here are some straightforward solutions to help you fix the common errors.

One of the main errors you might encounter is the ORA-24806 LOB form mismatch. This usually happens because of a character set mismatch between your source and target databases. For example, if your Oracle database uses WE8MSWIN1252 encoding and your PostgreSQL database defaults to UTF8, the difference in character sets can cause CLOB operations to fail. To resolve this, it’s best to standardize your source database to use UTF8 encoding. Then, make sure you configure your DMS source endpoint correctly, adding the right connection settings to handle character set conversion properly. This can involve specifying character set mapping parameters in your DMS endpoint settings.

Another frequent issue is the “Converter not found” error, which occurs because PostgreSQL’s WIN1252 encoding isn’t directly supported by AWS DMS. DMS expects standard PostgreSQL encodings, and WIN1252 isn’t included in the list of supported source encodings for DMS. To fix this, switch your PostgreSQL database to UTF8 encoding, which is a widely accepted standard and compatible with DMS migration tasks.

Here are some practical steps to improve your setup:

Switch your PostgreSQL database to UTF8 encoding. Keep your database in this encoding throughout the migration.
Properly configure your DMS source endpoint. Add specific connection attributes if needed, so that character set conversions happen smoothly.
Check the data types in your database, especially CLOB columns. Make sure they are compatible between PostgreSQL and Oracle to prevent mapping issues that can cause the migration task to fail.
Ensure your DMS replication instance has enough resources—memory and processing power—to handle the data load. Insufficient capacity can lead to errors and slowdowns.
Use CloudWatch logs to troubleshoot errors. Search for messages like “]E:” or “]W:” to find details about where and why the failure is happening. This insight can help you pinpoint whether the problem lies with source capture, target apply, or data conversion.

The root cause of many of these errors is the unsupported WIN1252 encoding in DMS. Making the switch to UTF8 on PostgreSQL and working closely with AWS Support can help you set up the character set handling properly. This approach ensures a smoother migration without data loss or errors.

For more detailed guidance, you can visit the AWS documentation on troubleshooting DMS issues here: AWS Re:Post – Troubleshoot AWS DMS replication task failures.