11 Durable executions
This chapter covers
- Short-running versus long-running processes
- Failure-free definitions
- Failure-tolerant executions
- Sagas versus durable executions
Durable executions, an emerging concept in software engineering, are to distributed systems what transactions are to databases: an abstraction concealing the possibility of failure.
“In the presence of partial failure, even the most basic rules for reasoning about computations do not hold.”
—An Equational Theory for Transactions (https://lampwww.epfl.ch/~cremet/publications/fsttcs03.pdf)
11.1 The Pitfalls of Partial Executions
Imagine a user registering for a streaming platform—for example, for video or music streaming. During the registration process, the platform handles the user's credit card payment and then grants access to its content library. Listing 11.1 displays the steps involved in the signup function.
Listing 11.1 User signup function
async function signup(user) {
const charge = await Payment.create({
...
});
💀 #A
const account = await Account.create({
...
});
}
At first glance, the function may appear to be fine. However, upon closer inspection, we notice a problem: the function only handles the Happy Path, naively ignoring the possibility of failure. If the function crashes after charging the credit card but before updating the database; that is, if the function executes partially, the user will be charged but will not have access.