until you have filled your ram, you can feel free to put anything to hashtable.
Since hashtable has its indexes accessed by integers, the real limit is 4,294,967,295 * 4,294,967,295 entries per hashtable, and you can have up to 255 hashtables in one map.
This sums up to 4,703,919,736,605,502,341,375 available entries. You will run out of RAM far far before that