This is not metrics, this is logs. Logs contain a lot of detail that are not appropriate for metrics. Logs output tends to be expensive, it costs a lot of time

This is not metrics, this is logs. Logs contain a lot of detail that are not appropriate for metrics. Logs output tends to be expensive, it costs a lot of time and IO to emit, compress, send, store logs. Logs also tend to contain PII things. Usernames, IP addresses, trace IDs, etc. We don't want that kind of cardinality in metrics. Metrics are another thing. They tend to be internal counters inside a single process. With multi-threaded languages like Go, Java, C++, we can track metric data in memory very efficiently. For metrics, see https://openmetrics.io/ https://openmetrics.io/