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

If you must use Java, then implement your own hashtable/hashmap. An important property of your table is to use a linkedlist to handle collisions. Hence when you do a lookup, you may return all the elements on the list.