B-Trees are quite popular in-memory structures when focusing on performance. I expect the others could be adapted as well (and likely have been). A quick goog

B-Trees are quite popular in-memory structures when focusing on performance. I expect the others could be adapted as well (and likely have been). A quick google turns up http://www.cs.cmu.edu/~chensm/papers/fpbtree.pdf http://www.cs.cmu.edu/~chensm/papers/fpbtree.pdf