Worker Pools

Consider a typical incident, described here as an example rather than a measured case. A team writes a program to fetch 5,000 product pages from an internal service that accepts at most a few hundred connections at once. The first version starts one goroutine per URL, since goroutines are cheap. All 5,000 requests arrive at the service within a few milliseconds, the service refuses most of them, and most of the run ends in errors.

The second version starts 20 goroutines and gives them the URLs through one channel