... or you're Google and have a database in the hundreds or thousands of TB and literally have to write your own database (they went from almost inventing mapreduce, to going full circle back to full scale distributed RDBMS SQL with F1, which I wish they'd open source),
You may be interested in CockroachDB, which was inspired by Google's F1 and Spanner implementations.
https://www.cockroachlabs.com/
Another contender was FoundationDB, but Apple bought them and stopped selling it as a product.