What is the y-axis of this Oracle ASH Viewer? I am investigating different monitoring software for my database, and I stumbled upon this open source ASH Viewer. I noticed in the main graph on the y-axis for resource usage, it's labeled as "Active Sessions" with an axis of varying integers

Link: https://github.com/akardapolov/ASH-Viewer#how-it-works



I don't understand what "Active Sessions" is supposed to mean. Is this the CPU % utilization of the database?
Since the link you included says the data is taken from V$ACTIVE_SESSION_HISTORY, presumably these are the wait event classes. In other words, the diagram shows how many sessions are waiting on each event class or actively executing ("CPU used") at any given time.