How to force Minecraft to use more ram to decrease lag?

Solution 1:

The -Xmx 4G option simply determines the maximum amount of memory that Minecraft can use, it does not mean that Minecraft are forced to use that amount of memory.

If you want to force Minecraft to use that amount of memory, you should use -Xms instead of -Xmx. This is the option that forces Minecraft to use that amount of memory (actually, this is simply an option to let Minecraft reserve a specified amount of memory and use it from there when needed.)

It's important to note that -Xmx must have a value equal to or greater than the value set in -Xms. For example, if the -Xms value is 4G (-Xms 4G), then the -Xmx value must also be 4G or higher.

So, -Xms 4G -Xmx 4G or -Xms 4G -Xmx 8G.