The game freezes when you agro high amounts of pigmen.
The redstone stuff stop working the entieties stop mving, but you can sorta move around, heavy lag.

Acording to https://twitter.com/Panda4994/status/681999441662885888 Is the AI

This does not happen in 1.8 only in the 1.9 snapshots. as you can see in both of th version I attached,

In 1.8 I get about 20 fps and the farm works, just fine. With more than 50% extra juice in my cpu and memory.

In 1.9 I get no fps the game freezes but I can move sorta, And I still have more than 50% extra juice in the memory and cpu, the game just stops.
Until you go on creative and it will slowly come back alive.