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Your Migration Passed Every Test. Then the Database Started Taking 100× Longer.
How a seemingly harmless identifier change can expose hidden database bottlenecks in production.
Imagine you’re working on a backend service that processes millions of orders, payments, or transactions.
For months, your database has been performing reliably. A query joining orders with customers takes approximately 5 milliseconds. Indexes are in place, query plans look healthy, and the application meets its latency targets.
Then your team makes a seemingly reasonable architectural decision.
You replace string-based primary keys with UUIDs.
The migration completes successfully. Row counts match. Foreign keys remain valid. Indexes exist. Integration tests pass. The application starts without errors.
Everything looks good.
Until production traffic arrives.
A query that previously took 5 milliseconds now takes 500 milliseconds.
The same tables. The same relationships. The same logical data. The same query.
Your database has suddenly become 100 times slower.
The first reaction is predictable: UUIDs must be slower than strings.
