Messages in this thread | | | Date | Sat, 1 Nov 2008 10:17:41 +0000 | From | Sean Young <> | Subject | Re: [RFC] B+Tree library |
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On Sat, Nov 01, 2008 at 12:36:15AM +0100, Joern Engel wrote: > On Fri, 31 October 2008 20:17:45 +0000, Sean Young wrote: > > On Sun, Oct 26, 2008 at 01:46:44PM +0100, Joern Engel wrote: > > > General advantages of btrees are memory density and efficient use of > > > cachelines. Hashtables are either too small and degrade into linked > > > list performance, or they are too large and waste memory. With changing > > > workloads, both may be true on the same system. Rbtrees have a bad > > > fanout of less than 2 (they are not actually balanced binary trees), > > > hence reading a fairly large number of cachelines to each lookup. > > > > Which reminds me: > > > > find_vma() uses rbtrees. Now I assume find_vma() is called far more than > > mmap() and friends. Since avltree are balanced (unlike rbtrees) lookups > > will be faster at the expense of extra rotations during updates. > > Maybe I should have been clearer. Rbtrees _are_ balanced trees. They > are not balanced _binary_ trees, but balanced 234-trees in a binary > representation.
I should have been more clearer. avltrees are more rigidly balanced than rbtrees, making them faster for lookups but slower for modification:
http://en.wikipedia.org/wiki/AVL_tree#Comparison_to_other_structures
The difference between the shortest path to a leaf node and the longest path to a leaf node is +1 for avl and *2 for red-black.
Sean
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