What is the difference between the rate() and increase() functions in PromQL?

In PromQL, the functions rate() and increase() work with counters but serve different purposes:

• rate() calculates the average rate of change of a counter over a specified time interval. It returns the value in units of change per second. This is useful when you need to know the speed of events, such as requests per second.

• increase() calculates the total increase in the counter's value over a specified time interval. It returns the absolute number of increases over the period.

Example:

rate(http_requests_total[5m])

Returns the average number of requests per second over the last 5 minutes.

increase(http_requests_total[5m])

Returns the total number of requests over the last 5 minutes.

Thus, rate() is convenient for monitoring speed, while increase() is used for counting the total number of events over a period.