Affects Version/s: Minecraft 1.13-pre8
Fix Version/s: Minecraft 1.13-pre9
Loading up a (specific?) 1.12 world in 1.13 renders the world laggy and unplayable. Setting the render distance to minimum and leaving the world to process for five minutes shows no sign of improvement in world performance.
Creating a new 1.13 world immediately shows good performance.
Attached are videos demonstrating both of these tests, as well as a world download that has not been opened in 1.13.
|World||World Create/Upgrade Time||Door Close Time|
|1.12 (Upgaded)||44 seconds||~ 9 seconds|
|1.13 (New)||17 seconds||~ 1 second|