Connection pooling is the most obvious one which is so common it tends to be transparent and built into many DB access libraries. Then there are all sorts of proxies/load balancers/multiplexors. If you think about it, the bits of code that handle web requests in your typical web app/framework/whatnot are very much like lambdas and when you write those, you generally don't have to worry about the cost of DB connections because it's a well-solved problem.