A Timer is used to measure how long (in seconds) some event is taking. Two types of Timers are supported:
Timer: for frequent short-duration events.
LongTaskTimer: for long-running tasks.
The long-duration Timer is setup so that you can track the time while an event being measured is still running. A regular Timer just records the duration and has no information until the task is complete.
As an example, consider a chart showing request latency to a typical web server. The expectation is many short requests, so the timer will be getting updated many times per second.
Now consider a background process to refresh metadata from a data store. For example, Edda caches AWS resources such as instances, volumes, auto-scaling groups etc. Normally, all data can be refreshed in a few minutes. If the AWS services are having problems, it can take much longer. A long duration timer can be used to track the overall time for refreshing the metadata.
The charts below show max latency for the refresh using a regular timer and a long task timer. Regular timer, note that the y-axis is using a logarithmic scale:
Long Task Timer: