Chapter 4, Prometheus Metrics Fundamentals

1. Time series data can be defined as a sequence of numerical data points collected chronologically from the same source – usually at a fixed interval. As such, this kind of data, when represented in a graphical form, will plot the evolution of the data through time, with the x-axis being time and the y-axis the data value.
2. A timestamp, a value, and tags/labels.
3. The write-ahead log (WAL).
4. The default is 2h and should not be changed.
5. A float64 value and a timestamp with millisecond precision.
6. Histograms are especially useful for tracking bucketed latencies and sizes (for example, request durations or response sizes) as they can be freely aggregated across different dimensions. Another great use is to generate heatmaps (the evolution of histograms over time).
   Summaries without quantiles are quite cheap to generate, collect, and store...