Intro transaction concept

[sre-is-laura]

We talk about txns but don't explain them

immersive-go-course/primers/distributed-software-systems-architecture/state.md

Line 40 in 8df2ee4

In the first case, your primary datastore can handle the increased read load and the only consequence for your application will be an increase in duration of requests served. Your application will also consume additional system resources: it will hold more open transactions to your primary datastore than usual, and it will have more requests in flight than usual. Over time your cache service fills with a useful working set of data and everything returns to normal. Some systems offer a feature called _[cache warmup](https://github.com/facebook/mcrouter/wiki/Cold-cache-warm-up-setup)_ to speed this process up.