I agree that redis can handle some query volumes and client counts that postgres can't.

But FWIW I can easily saturate a 10GBit ethernet link with primary key-lookup read-only queries, without the results being ridiculously wide or anything.

Because it didn't need any setup, I just used:

  SELECT * FROM pg_class WHERE oid = 'pg_class'::regclass;

I don't immediately have access to a faster network, connecting via tcp to localhost, and using some moderate pipelining (common in the redis world afaik), I get up to 19GB/s on my workstation.