Installing Sampler

Sampler is a mod by Player that generates .nps files.

You can find the forum thread over at IndustrialCraft Thread

For Minecraft 1.12


For Minecraft 1.11


For Minecraft 1.10


Running Sampler

Then you can /sampler start and /sampler stop while it's lagging.

Then a simple /sampler export [name of exported nps file here] will write out the .nps file that can be read by the developers in VisualVM.

Important: where to run Sampler?

Is it a lag issue on the server, like tick lag? Run Sampler on the server, NOT on your client!

Is it a lag issue on the client, like FPS lag? Run Sampler on the client, NOT on your server!

Source: Here