I used a foreign data wrapper to query elasticsearch indexes from within postgres.[0]

It pushed alot of complexity down away from higher-level app developers not familiar with ES patterns.

[0]: https://github.com/matthewfranglen/postgres-elasticsearch-fd...

one place they are great in production is as part of a data migration. if you have an old database system with application code on top that you want to move to pure postgres, fdws provide a way to incrementally rewrite the application logic without ever having to do a hard cutover.