At what point does it become “big data”? 10s of billions, 100s of billions? I would love to get a single PostgreSQL server to index all of my data in a timely m

At what point does it become “big data”? 10s of billions, 100s of billions? I would love to get a single PostgreSQL server to index all of my data in a timely manner. Heck, I’d be happy with a sharded scheme, if it worked. But, I don’t have time to learn the low-level details of a RDBMS and my system IO throughput to make that work. Spark works, it’s easy, and it’s relatively cheap. So, why make it more complicated?