Looking at cloud databases has me thinking about the speed of light. Wikipedia says that the speed of light is about 186,000 miles per second. If my calculations are correct that is 5.37 microseconds per mile. The United States is about 2680 miles wide so it would take light about 14.4 milliseconds to cross the US. If I ping one of my favorite web sites it takes tens of milliseconds to ping so that kind of makes sense because those sites are in other cities and I am going through various routers. I did some tests with my company’s storage and found that reading from our storage when the data is cached in the storage server takes around 200 microseconds. That is 200 microseconds for a round trip. I’m sure that our database servers and storage are a lot less than a mile apart so most of that time has nothing to do with the speed of light. I heard about a cloud vendor whose fast network connection took 100 microseconds plus the speed of light. I guess 100 microseconds is the cost of getting your data to fiber and light does the rest. If your cloud database was on the other side of the country, I guess it could take 14 milliseconds each way at least for each SQL request. If the cloud database was in your own city and say 10 miles away that would only tack on about 53.7 microseconds each way to the 100 microseconds overhead. I guess it makes sense. Maybe 100 microseconds plus the speed of light is the cost of moving data in the best case?