In my article about Robin Hood hashing [1], I had reached the conclusion that the Robin Hood hashing algorithm was performing poorly after deletions had occurred in the hash table, and I was quite disappointed with my results. In the research I had done, I had stumbled upon an article by Paul Khuong who had done some work on Robin Hood hashing [2], and I decided to email him to ask what he thought of my results. Paul got back to me, and after looking at my code on Github, he suggested that the performance could be greatly improved with only a little change to the removal method. He even submitted a patch to point out what the change would be, and he ran this modified version himself on the test cases I had included in the source code. The results he got were looking really good, and therefore I had no other choice but to write a follow-up article to present the change to the code and show those results.
In this article, I am presenting the backward shift deletion variant for the Robin Hood hashing algorithm. I start by explaining what backward shift deletion is and how to implement it, then I use it on the same test cases that I had run in my previous article. Finally, I discuss the new results.
