Logs, metrics and traces
Also called Telemetry, Spans, The three pillars
Three kinds of signal. A log is a timestamped event. A metric is a number over time, such as requests a second. A trace follows one request through every call it makes.
They answer different questions: a metric says something is wrong, a trace says where, and a log says what happened there. Give an agent only one of them, and it will guess at the rest.
Say it to your agent
“Checkout p95 went from 300 ms to 900 ms on Tuesday. Pull one slow trace and one normal trace, and compare them span by span. Tell me which span grew, then find the log lines for that trace id. Don't guess from the code until you have the trace.”