Determining the sales tax rate at a given address is an expensive operation. Our team has written a function called sales_tax_lookup, that takes a street address as a parameter and returns the sales tax rate, but it is slow to return a result.
While there are billions of addresses, we've identified that 95% of lookups come from a relatively small number of addresses (less than 100K addresses). Unfortunately, you won't know what these addresses are in advance.
You have been tasked with writing a caching layer, with a constraint that the cache can only be large enough to store approximately 50K addresses. Your goal is to produce a function "fast_rate_lookup" that returns the same results as "sales_tax_lookup", but with better performance.
- Optimize for the fewest number of calls to sales_tax_lookup while still maintaining full functionality.
- It is okay for the cache to start empty, and to fill over time. There is no need to pre-warm the cache when the server reboots.
- Assume this will run on a single server, and that the cache can be stored in program memory (i.e., a persistent variable is okay for the exercise).
This code is written using NodeJS and ImmutableJs. You can run it locally using npm install. Output is inside the NodeJS terminal window