If we’ve gotta take the database down for maintenance – perhaps a version upgrade, perhaps upgrading our own code, maybe scaling up the hardware – when’s the best time to do it?
For this week’s query exercise, the business has asked us to identify 3 1-hour periods with the least user activity, in this format:
- Mondays, 1:00-1:59
- Saturdays, 23:00-23:59
- Sundays, 2:00-2:59
Pop open the Stack Overflow database, and for the sake of simplicity for this exercise:
- We’re just going to look at the users table. We’ll judge load by times when the fewest number of users are created, judging by the users.creationdate column.
- We’re not dealing with time zones.
- We’re only looking for one-hour time ranges that start with 00 and end with 59, like 1:00-1:59. We’re using a little shorthand there and not typing out the seconds, but the point is that we don’t want you saying “the best time is 2:15:05 to 3:14:04.” That’s delightfully ambitious – but let’s keep it simple here. Not everyone has as much free time as you, bud.
Pick a 28-day window so that you’re looking at several weeks of trending activity, and come up with your one-hour preferences. (I expect folks to come up with widely different answers depending on which 28-day window they pick, and which copy of the database they’re using. That’s okay! The goal is to write the query, and then check your logic against the gotchas that I discuss next week.)
The performance of your query isn’t a concern here – this isn’t a query we’ll be running on a regular basis. We just need to know the quietest times in the database.
You can post your answers in this blog post’s comments, and discuss each others’ ideas. We’ll revisit your answers next week. Have fun!