I am currently working on building a Pigman farm on my multiplayer server. I have been testing it out in a single player world to make sure that everything will run smoothly. There is one problem when I activate the farm, seeing as there are so many pigmen being aggroed at once, the game decides to slow right down. The pigmen move slower than usual, and its almost like the game is struggling to keep up with the amount of updates that are happening at once. When I switch into creative mode and the pigmen are no longer tracking me, the game seems to catch up to itself and they run around like mad for 5 seconds or so until they are in the proper position that they should be in. This farm works perfectly fine in 1.8 and runs smoothly.

I have also experienced some of the same lag issues when on my server, where mobs will be incredibly jittery and not run as smoothly as they should. As well, it takes forever to eat food. This could be due to the fact that we have farms running in the spawn chunks, and we are on a purely vanilla server. This has only started to arise when we switched over to 1.9.

Attached will be a forced crash report of the game while the farm is running. And while it isn't.