What does Heap Usage mean in PM2

Question

What does Heap Usage mean in the "Custom Metrics" window when running pm2 monit?

The value for my server gets dangerously close to 100%.

Gollin

It looks like used heap size / heap size (41/57 = 72%). Ideally in an efficiently written program it would be 100% or close to 100% because that would mean that all malloc'd memory is actually used rather than simply allocated but not used – Kantar

Why is 100% better? Because malloc'd memory is not available to other programs. Consider a PC with 4GB of ram and your heap is 3GB - that leaves only 1GB free RAM. But if heap usage is only 10% that means your program is only using 300MB but allocates (makes unavailable to other programs) 3GB wasting 2.7GB of RAM unused and unusable – Kantar

@Kantar The way you phrased that confused me for a moment. I didn't realize you were posing a question for rhetorical purposes instead of asking! – Farceur

Answer 1

The heap is a memory used by programming languages to store global variables. By default, all global variable are stored in heap memory space.

It`is maybe because of your programs variable.

you can reset it after it exceeded the limit or force pm2 do it for you automatically.

pm2 start api.js --max-memory-restart 300M

Protomartyr