Just downloaded the 18w19b snapshot yesterday.  Created a new world last night and played for a few hours.  Left it running overnight while I slept.  Woke up this morning.  Ended up closing the game down to restart my computer.  Now I can't load up the world I made last night.  It gets into the world, and then as it is starting to display the world the game disappears.  I attached some of the logs.  It seems to run out of memory.