Java On-Memory Efficient Key-Value Store

Question

I have store 111 million key-value pairs (one key can have multiple values - maximum 2/3) whose key are 50 bit Integers and values are 32 bit (maximum) Integers. Now, my req

Answer 1

Is there any Java library which satisfies my all those needs properly.

AFAIK no. Or at least, not one that minimizes the memory footprint.

However, it should be easy write a custom map class that is specialized to these requirements.