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change the way that these functions ascend the tree when the search for a matching leaf fails at an interior node. Rather than returning to the root of the tree and repeating the lookup with an updated key, maintain a stack of interior nodes that were visited during the descent and use that stack to resume the lookup at the closest ancestor that might have a matching descendant. Sponsored by: EMC / Isilon Storage Division Reviewed by: attilio Tested by: pho