Data Centers: The Backbone of Modern Databases
Concept. Latency in a modern data center spans eight orders of magnitude, from a nanosecond on-chip to a hundred milliseconds across the planet. An algorithm's cost depends on which tier holds its data.
Intuition. A SELECT against a 10-billion-row Listens table doesn't run on one machine. It runs in a data center the size of a Costco, and the same byte can be a nanosecond away or a hundred milliseconds away depending on where it sits. Everything this course does about cost comes out of that gap.
Latency Tiers
On-chip is nanoseconds. Memory is hundreds of nanoseconds. Storage is tens of microseconds. Disk and the network next door are milliseconds, and the far side of the planet is a hundred of them. Every algorithm in this course is implicitly priced against that ladder; Storage & Paging puts exact numbers on the storage half.
Figure 1. Seven tiers in one data center, fastest to slowest, from L1 cache at 1 ns to a cross-continent round trip at 100 ms. End to end is 100,000,000x, eight orders of magnitude, and a read from the wrong tier costs up to 10,000,000x more.
Why a Database Course Cares
Every cost model we will use, every page-count argument, every join algorithm, is shaped by this hierarchy. A query plan is a routing decision: which tier do you read from, how often, and in what order. Get the tier right and a billion-row query finishes in seconds. Get it wrong and the same query never finishes.
Google Data Centers
This is where BigQuery, Cloud SQL, and Spanner physically run.
Microsoft Azure Documentary
A behind-the-scenes tour of where your data physically lives.