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This seems to gloss over the actual rewrite. How did you ensure queries were equivalent? How did you configure the product to be able to read from and write to both databases? Did migrating reveal any bugs? Were you largely able to port your queries 1:1?

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You can write logging for both drivers dumping results.

Then checking which query doesn't return the same result set.

Hopefully they had comprehensive test coverage. That would have helped greatly in that regard.

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