Skip to main content

MongoDB System Alert: Potential Relational Migrator data loss issues

Written by Clevyyy

Issue Description

  • Date announced: May 14, 2026

  • Impact:

    For users that have migrated with Relational Migrator:

    • Sharded cluster migrations with embedded documents or embedded arrays may cause missing documents.

    • Cyclic mappings with an excluded foreign key under an embedded array will be missing.

    • A source table column used in multiple composite foreign key relationships can cause mismatched embeddings.

    • Conflicting field name choices can cause omitted and mis-named fields.

  • Versions: MongoDB Relational Migrator prior to 1.16.0

Details

We’ve identified four data integrity issues in the MongoDB Relational Migrator (RM) tool. In the specific scenarios described below, these issues may result in data loss or corruption without a visible error message.

These defects impacted all versions of Relational Migrator.

You may be impacted if you have migrated data with RM in any of the following ways:

  1. The destination is a sharded cluster and your target schema contains embedded documents or embedded arrays.

  2. A table is mapped to more than one collection in the target schema.

  3. A source table column is used in multiple composite foreign key relationships (for example, foreign keys consisting of multiple columns).

  4. Any fields in the target schema have been renamed to have the same name as a different source column.

The Relational Migrator version 1.16.0 fixes scenarios 2-4 listed above. Migrations to sharded clusters have been temporarily disabled while we address the first issue.

Action Items

If you believe any of the situations above impact your RM projects:

  1. Prioritize checking the affected collections for missing or incorrect data.

  2. Plan to re-migrate any affected collections using Relational Migrator version 1.16.0.

  3. If you’re unsure whether you’re affected or how to check, open a case (if you have an active support plan) or start a chat with MongoDB Support so we can help you confirm and plan next steps.

For more information regarding each issue, see the following tickets:

  • SERVER-126523 - Sharded cluster migrations with embedded documents or embedded arrays may cause missing documents. Affects Relational Migrator versions <1.16.0.

  • SERVER-126528 - Cyclic mappings with an excluded foreign key under an embedded array will be missing. Affects Relational Migrator versions 1.14.1 to 1.15.2 inclusive.

  • SERVER-126529 - Source table column used in multiple composite foreign key relationships can cause mismatched embeddings. Affects Relational Migrator versions <1.16.0.

  • SERVER-126530 - Conflicting field name choices can cause omitted and mis-named fields. Affects Relational Migrator versions <1.16.0.

If you have any questions or need to confirm whether you have been affected, open a support case or start a chat with the MongoDB Support team.

Did this answer your question?