There are instances in life when isolation is actually welcome. One of those instances pertains to the I in the acronym ACID, which outlines the key properties necessary to maintain the integrity of transactions in a database. The time series database (TSDB) embedded in the Prometheus server has the C (consistency), the D (durability), and – somewhat debatable – the A (atomicity). But up until and including Prometheus v2.16, it did not have the I (isolation).
Last year, the Skylight team gave a talk called Inside Rails: The Lifecycle of a Request. In that talk, we covered everything that happens between typing a URL into your browser to a request reaching your Rails controller action. But that talk ended with a cliffhanger: Once we are in the controller action, how does Rails send our response back to the browser?