Fellow computer-napkin-mathers, it's time for napkin problem #2. The last problem's solution you'll find at the end! I've updated

sirupsen/napkin-math with last week's tips and tricks--consult that repo if you need a refresher. My goal for that repo is to become a great resource for napkin calculations in the domain of computers. My talk from SRECON's video was published this week, you can see it

here.
**Problem #2: Your SSD-backed database has a usage-pattern that rewards you with a 80% page-cache hit-rate (i.e. 80% of disk reads are served directly out of memory instead of going to the SSD). The median is 50 distinct disk pages for a query to gather its query results (e.g. InnoDB pages in MySQL). What is the expected average query time from your database?**
Reply to this email with your answer, happy to provide you mine ahead of time if you're curious.

**Last Problem's Solution**
**Question: ****How much will the storage of logs cost for a standard, monolithic 100,000 RPS web application?**
**Answer: **First I jotted down the basics and convert them to scientific notation for easy calculation

*~1*10^3 bytes/request (1 KB), 9 * 10^4 seconds/day, and 10^5 requests/second.* Then multiplied these numbers into storage per day:

*10^3 bytes/request * 9 * 10^4 seconds/day * 10^5 requests/second = 9 * 10^12 bytes/day = 9 Tb/day. Then we need to use the monthly cost for disk storage from sirupsen/napkin-math (or your cloud's pricing calculator) -- $0.01 GB/month. So we have 9 Tb/day * $0.01 GB/month. We do some unit conversions (you could do this by hand to practise, or on Wolframalpha) and get to $3 * 10^3 per month, or $3,000 per month. Most of those who replied got somewhere between $1,000 and $10,000 -- well within an order of magnitude!*