Data Centers: The Backbone of Modern Databases
Concept. Latency in a modern data center spans seven orders of magnitude, from L1 cache at 1 ns to a cross-continent round trip at 100 ms, and an algorithm's cost depends entirely on which tier its data lives in.
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 cost of every read depends on which tier the data lives in, L1 cache (1 ns), RAM (100 ns), SSD (100 µs), or cross-continent network (100 ms). Seven orders of magnitude.
Latency Tiers: Seven Orders of Magnitude
Inside one data center the same byte can be a nanosecond away or a hundred milliseconds away, depending on which tier it lives in. Every algorithm in this course is implicitly priced against this ladder.
Figure 1. Seven latency tiers in one data center, ordered fastest to slowest: L1 cache at 1 ns up to a cross-continent round trip at 100 ms. End to end is 100,000,000x, and a read from the wrong tier costs up to 10,000,000x more. The rest of the course prices every page-count and join argument against this ladder.
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
These are the nerve centers for BigQuery, Cloud SQL, and Spanner. Each query you run is a tiny cog in this vast machine.
Microsoft Azure Documentary
A behind-the-scenes tour of where your data physically lives.