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The Two-Database Bug That’s Breaking More RAG Apps Than You’d Think
How to stop your vector database from falling out of sync with your DB (PostgreSQL) — a step-by-step guide to the Transactional Outbox Pattern in FastAPI.
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Wanjiru, a full-stack dev, is having a nightmare scenario: a user deleted a document three hours ago, and it just showed up in a chatbot answer, quoting a pricing sheet that was supposed to be deleted.
She checks Postgres, the row is gone as it should be, then checks the vector store and finds the old embedding still sitting there, ready to be retrieved. Nothing threw an error, so the team didn’t know until the user complained.
In This Article:
Like the issue above, two databases, the main Postgres DB and the vector DB, can fall out of sync, and there’s no alert to tell the team when it happens.
The fix explored in this article is the Transactional Outbox Pattern. Simply put, it means writing the update and a note describing what needs to sync, in the same transaction, inside the same database. The actual sync to the vector database still happens afterward, but now there’s a permanent record making sure it never gets skipped or lost.
