Quicksave-Quickload addon for CubicChunks
Quickly restore state of a Minecraft from a single checkpoint. For single- and multi-player game.
First download and install CubicChunks from this place: https://minecraft.curseforge.com/projects/opencubicchunks
In server use command /q [save|load]
In client use buttons in pause menu or same commands.
A more often you will save a game - a less memory will be occupied. Not logged players will not be affected by load and save events. If you travel to another dimension after you saved a game - you will be teleported back. Of course saves persist across game sessions.