Best Answer
As Tim said, use that command to let opis diagnose. Also, try my lengthy data finding post that tim beat me to, so we know exactly if it's using a bunch of resources.
Assuming you have windows:
Hit F3 in game. Look at the allocated ram and ram USAGE. What are they?
Open task manager. Open the game to lan (so it doesn't pause when you close) and minimize minecraft.
Go to the task manager Performance page, like so
Now, look at this. See the highlighted things, and the things with the arrows? Tell me what those are.
Now, we're gonna go to the PROCESSES tab.
We're gonna look for the game, and see how much RAM it's using.
Look for this in your processes tab. How much ram are they using?
"Data, data, data, i cannot make bricks without clay."
Used memory 33% - 920mb - was lowest when I recorded it, it goes up to about 46-54% and then resets to 33%.
Allocated memory 56% - 1544mb
Cpu usage - 73%-80% (average around 75%) (3.23Ghz)
Memory - 4.9Gb out of 5.9Gb (83%)
Memory
6.0 GB DDR3
Speed: 1333 MHz
Slots used: 2 of 2
Form factor: DIMM
Hardware reserved: 118 MB
Available 1.1 GB
Cached 1.0 GB
Committed 6.4/8.9 GB
Paged pool 270 MB
Non-paged pool 95.3 MB
In use 4.8 GB
In the task manager window:
Top process javaw.exe uses 237,312 K
Bottom process javaw.exe uses 2,547,544 K
Actually while figuring this out my minecraft was on and it seems it started to get a little bit less buggy. I'd say instead of being 10 times slower, now its just 50% of its normal speed. (In that time I did absolutely nothing to my minecraft world).
Hope this info helps. And thanks for your time.
Edit:
Ps, I'm not quite sure what Tps means but I don't seem to have opis. I used /cofh tps and it didn't show any abnormal activity in any of my worlds.
Edit2:
Just started working fine all of a sudden... No idea why.