"searching through around 200 million tuples within the order of 2 seconds (partially stored columnar using psql array types and GIN indexes). Not for a second did I consider using any kind of specialized database, nor optimized algorithms, except for some application-level caching. "

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That's cool and all, but for some real-time applications, retrieving in the order of seconds is unacceptable.

DBMS has their earned place in the backend stack but I found that statement of covering 98% of the cases a bit of a stretch.