class PEROBS::BigTreeNode
The BigTreeNode
class provides the BTree
nodes for the BigTree
objects. A node can either be a branch node or a leaf node. Branch nodes don’t store values, only references to child nodes. Leaf nodes don’t have child nodes but store the actual values. All nodes store a list of keys that are used to naviate the tree and find the values. A key is either directly associated with a value or determines the lower key boundary for the following child node.
Public Class Methods
Internal constructor. Use Store.new(BigTreeNode, ...)
instead. @param p [Handle] @param tree [BigTree] The tree this node should belong to @param is_leaf [Boolean] True if a leaf node should be created, false
for a branch node.
@param parent [BigTreeNode] Parent node @param prev_sibling [BigTreeNode] Previous sibling @param next_sibling [BigTreeNode] Next sibling
PEROBS::Object::new
# File lib/perobs/BigTreeNode.rb, line 51 def initialize(p, tree, is_leaf, parent = nil, prev_sibling = nil, next_sibling = nil) super(p) self.tree = tree self.parent = parent self.keys = @store.new(PEROBS::Array) if is_leaf # Create a new leaf node. It stores values and has no children. self.values = @store.new(PEROBS::Array) self.children = nil else # Create a new tree node. It doesn't store values and can have child # nodes. self.children = @store.new(PEROBS::Array) self.values = nil end # Link the neighboring siblings to the newly inserted node. If the node # is a leaf node and has no sibling on a side we also must register it # as first or last leaf with the BigTree object. if (self.prev_sibling = prev_sibling) @prev_sibling.next_sibling = myself elsif is_leaf? @tree.first_leaf = myself end if (self.next_sibling = next_sibling) @next_sibling.prev_sibling = myself elsif is_leaf? @tree.last_leaf = myself end end
Public Instance Methods
Check consistency of the node and all subsequent nodes. In case an error is found, a message is logged and false is returned. @yield [key, value] @return [Boolean] true if tree has no errors
# File lib/perobs/BigTreeNode.rb, line 242 def check branch_depth = nil traverse do |node, position, stack| if position.zero? if node.parent # After a split the nodes will only have half the maximum keys. # For branch nodes one of the split nodes will have even 1 key # less as this will become the branch key in a parent node. if node.keys.size < min_keys - (node.is_leaf? ? 0 : 1) node.error "BigTree node #{node._id} has too few keys" return false end end if node.keys.size > @tree.node_size node.error 'BigTree node must not have more then ' \ "#{@tree.node_size} keys, but has #{node.keys.size} keys" return false end last_key = nil node.keys.each do |key| if last_key && key < last_key node.error 'Keys are not increasing monotoneously: ' \ "#{node.keys.inspect}" return false end last_key = key end if node.is_leaf? if branch_depth unless branch_depth == stack.size node.error 'All leaf nodes must have same distance from root' return false end else branch_depth = stack.size end if node.prev_sibling.nil? if @tree.first_leaf != node node.error "Leaf node #{node._id} has no previous sibling " \ 'but is not the first leaf of the tree' return false end elsif node.prev_sibling.next_sibling != node node.error 'next_sibling of previous sibling does not point to ' \ 'this node' return false end if node.next_sibling.nil? if @tree.last_leaf != node node.error "Leaf node #{node._id} has no next sibling " \ 'but is not the last leaf of the tree' return false end elsif node.next_sibling.prev_sibling != node node.error 'previous_sibling of next sibling does not point to ' \ 'this node' return false end unless node.keys.size == node.values.size node.error "Key count (#{node.keys.size}) and value " \ "count (#{node.values.size}) don't match" return false end if node.children node.error 'children must be nil for a leaf node' return false end else if node.values node.error 'values must be nil for a branch node' return false end unless node.children.size == node.keys.size + 1 node.error "Key count (#{node.keys.size}) must be one " \ "less than children count (#{node.children.size})" return false end node.children.each_with_index do |child, i| unless child.is_a?(BigTreeNode) node.error "Child #{i} is of class #{child.class} " \ 'instead of BigTreeNode' return false end unless child.parent.is_a?(BigTreeNode) node.error "Parent reference of child #{i} is of class " \ "#{child.class} instead of BigTreeNode" return false end if child == node node.error "Child #{i} point to self" return false end if stack.include?(child) node.error "Child #{i} points to ancester node" return false end unless child.parent == node node.error "Child #{i} does not have parent pointing " \ 'to this node' return false end if i.positive? && node.children[i - 1].next_sibling != child node.error 'next_sibling of node ' \ "#{node.children[i - 1]._id} " \ "must point to node #{child._id}" return false end if i < node.children.length - 1 && child != node.children[i + 1].prev_sibling node.error 'prev_sibling of node ' \ "#{node.children[i + 1]._id} " \ "must point to node #{child._id}" return false end end end elsif position <= node.keys.size # These checks are done after we have completed the respective child # node with index 'position - 1'. index = position - 1 if node.is_leaf? if block_given? # If a block was given, call this block with the key and value. return false unless yield(node.keys[index], node.values[index]) end else unless node.children[index].keys.last < node.keys[index] node.error "Child #{node.children[index]._id} " \ "has too large key #{node.children[index].keys.last}. " \ "Must be smaller than #{node.keys[index]}." return false end unless node.children[position].keys.first >= node.keys[index] node.error "Child #{node.children[position]._id} " \ "has too small key #{node.children[position].keys.first}. " \ "Must be larger than or equal to #{node.keys[index]}." return false end end end end true end
Iterate over all the key/value pairs in this node and all sub-nodes. @yield [key, value]
# File lib/perobs/BigTreeNode.rb, line 211 def each traverse do |node, position, _| node.is_leaf? && position < node.keys.size && yield(node.keys[position], node.values[position]) end end
Iterate over all the key/value pairs of the node. @yield [key, value]
# File lib/perobs/BigTreeNode.rb, line 220 def each_element return self unless is_leaf? 0.upto(@keys.length - 1) do |i| yield(@keys[i], @values[i]) end end
Print and log an error message for the node.
# File lib/perobs/BigTreeNode.rb, line 760 def error(msg) msg = "Error in BigTree node @#{@_id}: #{msg}\n" + @tree.to_s $stderr.puts msg PEROBS.log.error msg end
Return the value that matches the given key or return nil if they key is unknown. @param key [Integer] key to search for @return [Integer or nil] value that matches the key
# File lib/perobs/BigTreeNode.rb, line 114 def get(key) node = self while node # Find index of the entry that best fits the key. i = node.search_key_index(key) if node.is_leaf? # This is a leaf node. Check if there is an exact match for the # given key and return the corresponding value or nil. return node.keys[i] == key ? node.values[i] : nil end # Descend into the right child node to continue the search. node = node.children[i] end PEROBS.log.fatal 'Could not find proper node to get from while ' \ "looking for key #{key}" end
Return if given key is stored in the node. @param key [Integer] key to search for @return [Boolean] True if key was found, false otherwise
# File lib/perobs/BigTreeNode.rb, line 163 def has_key?(key) node = self while node # Find index of the entry that best fits the key. i = node.search_key_index(key) if node.is_leaf? # This is a leaf node. Check if there is an exact match for the # given key and return the corresponding value or nil. return node.keys[i] == key end # Descend into the right child node to continue the search. node = node.children[i] end PEROBS.log.fatal 'Could not find proper node to get from while ' \ "looking for key #{key}" end
Insert or replace the given value by using the key as unique address. @param key [Integer] Unique key to retrieve the value @param value [Integer] value to insert
# File lib/perobs/BigTreeNode.rb, line 91 def insert(key, value) node = myself # Traverse the tree to find the right node to add or replace the value. while node # All nodes that we find on the way that are full will be split into # two half-full nodes. node = node.split_node if node.keys.size >= @tree.node_size # Once we have reached a leaf node we can insert or replace the value. return node.insert_element(key, value) if node.is_leaf? # Descend into the right child node to add the value to. node = node.children[node.search_key_index(key)] end PEROBS.log.fatal 'Could not find proper node to insert into' end
Insert the given value or child into the current node using the key as index. @param key [Integer] key to address the value or child @param child_or_value [Integer or BigTreeNode] value or BigTreeNode
@return [Boolean] true if new element, false if override existing
element
# File lib/perobs/BigTreeNode.rb, line 475 def insert_element(key, child_or_value) if @keys.size >= @tree.node_size PEROBS.log.fatal "Cannot insert into a full BigTreeNode: #{@keys.size}" end i = search_key_index(key) if @keys[i] == key # Overwrite existing entries @keys[i] = key if is_leaf? @values[i] = child_or_value else @children[i + 1] = child_or_value end else # Create a new entry @keys.insert(i, key) if is_leaf? @values.insert(i, child_or_value) @tree.entry_counter += 1 else @children.insert(i + 1, child_or_value) end end end
@return [Boolean] True if this is a leaf node, false otherwise.
# File lib/perobs/BigTreeNode.rb, line 84 def is_leaf? @children.nil? end
# File lib/perobs/BigTreeNode.rb, line 589 def merge_with_branch_node(node) if @keys.length + 1 + node.keys.length > @tree.node_size PEROBS.log.fatal 'Branch nodes are too big to merge' end index = @parent.search_node_index(node) - 1 self.keys << @parent.keys[index] self.keys += node.keys node.children.each { |c| c.parent = myself } self.children += node.children node.parent.remove_child(node) end
# File lib/perobs/BigTreeNode.rb, line 578 def merge_with_leaf_node(node) if @keys.length + node.keys.length > @tree.node_size PEROBS.log.fatal 'Leaf nodes are too big to merge' end self.keys += node.keys self.values += node.values node.parent.remove_child(node) end
Return the node chain from the root to the leaf node storing the key/value pair. @param key [Integer] key to search for @return [Array of BigTreeNode] node list (may be empty)
# File lib/perobs/BigTreeNode.rb, line 138 def node_chain(key) node = myself list = [node] while node # Find index of the entry that best fits the key. i = node.search_key_index(key) if node.is_leaf? # This is a leaf node. Check if there is an exact match for the # given key and return the corresponding value or nil. return node.keys[i] == key ? list : [] end # Add current node to chain. list << node # Descend into the right child node to continue the search. node = node.children[i] end PEROBS.log.fatal "Could not find node chain for key #{key}" end
Return the value that matches the given key and remove the value from the tree. Return nil if the key is unknown. @param key [Integer] key to search for @return [Object] value that matches the key
# File lib/perobs/BigTreeNode.rb, line 187 def remove(key) node = self while node # Find index of the entry that best fits the key. i = node.search_key_index(key) if node.is_leaf? # This is a leaf node. Check if there is an exact match for the # given key and return the corresponding value or nil. return nil if node.keys[i] != key @tree.entry_counter -= 1 return node.remove_element(i) end # Descend into the right child node to continue the search. node = node.children[i] end PEROBS.log.fatal 'Could not find proper node to remove from' end
Remove the specified node from this branch node. @param node [BigTreeNode] The child to remove
# File lib/perobs/BigTreeNode.rb, line 532 def remove_child(node) unless (index = search_node_index(node)) PEROBS.log.fatal "Cannot remove child #{node._id} from node #{@_id}" end if index.zero? # Removing the first child is a bit more complicated as the # corresponding branch key is in a parent node. key = @keys.shift update_branch_key(key) else # For all other children we can just remove the corresponding key. @keys.delete_at(index - 1) end # Remove the child node link. child = @children.delete_at(index) # If we remove the first or last leaf node we must update the reference # in the BigTree object. @tree.first_leaf = child.next_sibling if child == @tree.first_leaf @tree.last_leaf = child.prev_sibling if child == @tree.last_leaf # Unlink the neighbouring siblings from the child child.prev_sibling.next_sibling = child.next_sibling if child.prev_sibling child.next_sibling.prev_sibling = child.prev_sibling if child.next_sibling if @keys.length < min_keys # The node has become too small. Try borrowing a node from an adjecent # sibling or merge with an adjecent node. if @prev_sibling && @prev_sibling.parent == @parent borrow_from_previous_sibling(@prev_sibling) || @prev_sibling.merge_with_branch_node(myself) elsif @next_sibling && @next_sibling.parent == @parent borrow_from_next_sibling(@next_sibling) || merge_with_branch_node(@next_sibling) end end if @parent.nil? && @children.length <= 1 # If the node just below the root only has one child it will become # the new root node. new_root = @children.first new_root.parent = nil @tree.root = new_root end end
Remove the element from a leaf node at the given index. @param index [Integer] The index of the entry to be removed @return [Object] The removed value
# File lib/perobs/BigTreeNode.rb, line 504 def remove_element(index) # Delete the key at the specified index. unless (key = @keys.delete_at(index)) PEROBS.log.fatal "Could not remove element #{index} from BigTreeNode @#{@_id}" end update_branch_key(key) if index.zero? # Delete the corresponding value. removed_value = @values.delete_at(index) if @keys.length < min_keys if @prev_sibling && @prev_sibling.parent == @parent borrow_from_previous_sibling(@prev_sibling) || @prev_sibling.merge_with_leaf_node(myself) elsif @next_sibling && @next_sibling.parent == @parent borrow_from_next_sibling(@next_sibling) || merge_with_leaf_node(@next_sibling) elsif @parent PEROBS.log.fatal 'Cannot not find adjecent leaf siblings' end end # The merge has potentially invalidated this node. After this method has # been called this copy of the node should no longer be used. removed_value end
Iterate over all the key/value pairs of the node in reverse order. @yield [key, value]
# File lib/perobs/BigTreeNode.rb, line 230 def reverse_each_element return self unless is_leaf? (@keys.length - 1).downto(0) do |i| yield(@keys[i], @values[i]) end end
Search the keys of the node that fits the given key. The result is either the index of an exact match or the index of the position where the given key would have to be inserted. @param key [Integer] key to search for @return [Integer] Index of the matching key or the insert position.
# File lib/perobs/BigTreeNode.rb, line 608 def search_key_index(key) # Handle special case for empty keys list. return 0 if @keys.empty? # Keys are unique and always sorted. Use a binary search to find the # index that fits the given key. li = pi = 0 ui = @keys.size - 1 while li <= ui # The pivot element is always in the middle between the lower and upper # index. pi = li + (ui - li) / 2 if key < @keys[pi] # The pivot element is smaller than the key. Set the upper index to # the pivot index. ui = pi - 1 elsif key > @keys[pi] # The pivot element is larger than the key. Set the lower index to # the pivot index. li = pi + 1 else # We've found an exact match. For leaf nodes return the found index. # For branch nodes we have to add one to the index since the larger # child is the right one. return is_leaf? ? pi : pi + 1 end end # No exact match was found. For the insert operaton we need to return # the index of the first key that is larger than the given key. @keys[pi] < key ? pi + 1 : pi end
# File lib/perobs/BigTreeNode.rb, line 641 def search_node_index(node) index = search_key_index(node.keys.first) unless @children[index] == node raise RuntimeError, "Child at index #{index} is not the requested node" end index end
Split the current node into two nodes. The upper half of the elements will be moved into a newly created node. This node will retain the lower half. @return [BigTreeNode] common parent of the two nodes
# File lib/perobs/BigTreeNode.rb, line 428 def split_node unless @parent # The node is the root node. We need to create a parent node first. self.parent = @store.new(BigTreeNode, @tree, false) @parent.children[0] = myself @tree.root = @parent end # Create the new sibling that will take the 2nd half of the # node content. sibling = @store.new(BigTreeNode, @tree, is_leaf?, @parent, myself, @next_sibling) # Determine the index of the middle element that gets moved to the # parent. The node size must be an uneven number. mid = @keys.size / 2 # Insert the middle element key into the parent node @parent.insert_element(@keys[mid], sibling) if is_leaf? # Copy the keys and values from the mid element onwards into the new # sibling node. sibling.keys += @keys[mid..-1] sibling.values += @values[mid..-1] # Delete the copied keys and values from this node. @values.slice!(mid..-1) else # Copy the keys from after the mid value onwards to the new sibling # node. sibling.keys += @keys[mid + 1..-1] # Same for the children. sibling.children += @children[mid + 1..-1] # Reparent the children to the new sibling parent. sibling.children.each { |c| c.parent = sibling } # And delete the copied children references. @children.slice!(mid + 1..-1) end # Delete the copied keys from this node. @keys.slice!(mid..-1) @parent end
Gather some statistics about the node and all sub nodes. @param stats [Stats] Data structure that stores the gathered data
# File lib/perobs/BigTreeNode.rb, line 687 def statistics(stats) traverse do |node, position, stack| if position.zero? if node.is_leaf? stats.leaf_nodes += 1 depth = stack.size + 1 stats.min_depth = depth if stats.min_depth.nil? || stats.min_depth < depth stats.max_depth = depth if stats.max_depth.nil? || stats.max_depth > depth else stats.branch_nodes += 1 end end end end
@return [String] Human reable form of the sub-tree.
# File lib/perobs/BigTreeNode.rb, line 392 def to_s str = '' traverse do |node, position, _| if position.zero? begin str += "#{node.parent ? node.parent.tree_prefix + ' +' : 'o'}" \ "#{node.tree_branch_mark}-" \ "#{node.keys.first.nil? ? '--' : 'v-'}#{node.tree_summary}\n" rescue => e str += "@@@@@@@@@@: #{e.message}\n" end else begin if node.is_leaf? if node.keys[position - 1] str += "#{node.tree_prefix} |" \ "[#{node.keys[position - 1]}, " \ "#{node.values[position - 1]}]\n" end elsif node.keys[position - 1] str += "#{node.tree_prefix} #{node.keys[position - 1]}\n" end rescue => e str += "@@@@@@@@@@: #{e.message}\n" end end end str end
This is a generic tree iterator. It yields before it descends into the child node and after (which is identical to before the next child descend). It yields the node, the position and the stack of parent nodes. @yield [node, position, stack]
# File lib/perobs/BigTreeNode.rb, line 655 def traverse # We use a non-recursive implementation to traverse the tree. This stack # keeps track of all the known still to be checked nodes. stack = [[self, 0]] until stack.empty? node, position = stack.pop # Call the payload method. The position marks where we are in the node # with respect to the traversal. 0 means we've just entered the node # for the first time and are about to descent to the first child. # Position 1 is after the 1st child has been processed and before the # 2nd child is being processed. If we have N children, the last # position is N after we have processed the last child and are about # to return to the parent node. yield(node, position, stack) next unless position <= node.keys.size # Push the next position for this node onto the stack. stack.push([node, position + 1]) if !node.is_leaf? && node.children[position] # If we have a child node for this position, push the linked node # and the starting position onto the stack. stack.push([node.children[position], 0]) end end end
Branch node decoration for the inspection method.
# File lib/perobs/BigTreeNode.rb, line 725 def tree_branch_mark return '' unless @parent '-' end
Return the decoration that marks the tree structure of this node for the inspection method.
# File lib/perobs/BigTreeNode.rb, line 704 def tree_prefix node = self str = '' while node is_last_child = false if node.parent is_last_child = node.parent.children.last == node else # Don't add lines for the top-level. break end str = (is_last_child ? ' ' : ' |') + str node = node.parent end str end
Text for the node line for the inspection method.
# File lib/perobs/BigTreeNode.rb, line 732 def tree_summary s = " @#{@_id}" if @parent begin s += " ^#{@parent._id}" rescue s += ' ^@' end end if @prev_sibling begin s += " <#{@prev_sibling._id}" rescue s += ' <@' end end if @next_sibling begin s += " >#{@next_sibling._id}" rescue s += ' >@' end end s end
Private Instance Methods
Try to borrow an element from the next sibling. @return [True or False] True if an element was borrowed, false
otherwise.
# File lib/perobs/BigTreeNode.rb, line 806 def borrow_from_next_sibling(next_node) if next_node.keys.length - 1 > min_keys # The next sibling now has a new lead key that requires the branch key # to be updated in the parent node. index = next_node.parent.search_node_index(next_node) - 1 if is_leaf? # Move the first key of the next node to the end of the this node self.keys << next_node.keys.shift # Register the new lead key of next_node with its parent next_node.parent.keys[index] = next_node.keys.first # Move the first value of the next node to the end of this node self.values << next_node.values.shift else # For branch nodes we need to get the lead key from the parent of # next_node. self.keys << next_node.parent.keys[index] # The old lead key of next_node becomes the branch key in the parent # of next_node. And the keys of next_node are shifted. next_node.parent.keys[index] = next_node.keys.shift # Move the first child of the next node to the end of this node self.children << (node = next_node.children.shift) node.parent = myself end return true end false end
Try to borrow an element from the preceding sibling. @return [True or False] True if an element was borrowed, false
otherwise.
# File lib/perobs/BigTreeNode.rb, line 775 def borrow_from_previous_sibling(prev_node) if prev_node.keys.length - 1 > min_keys index = @parent.search_node_index(self) - 1 if is_leaf? # Move the last key of the previous node to the front of this node @keys.unshift(prev_node.keys.pop) # Register the new lead key of this node with its parent @parent.keys[index] = @keys.first # Move the last value of the previous node to the front of this node @values.unshift(prev_node.values.pop) else # For branch nodes the branch key will be the borrowed key. @keys.unshift(@parent.keys[index]) # And the last key of the previous key will become the new branch # key for this node. @parent.keys[index] = prev_node.keys.pop # Move the last child of the previous node to the front of this node @children.unshift(node = prev_node.children.pop) node.parent = myself end return true end false end
# File lib/perobs/BigTreeNode.rb, line 768 def min_keys @tree.node_size / 2 end
# File lib/perobs/BigTreeNode.rb, line 837 def update_branch_key(old_key) new_key = @keys.first return unless (node = @parent) while node if (index = node.keys.index(old_key)) node.keys[index] = new_key return end node = node.parent end # The smallest element has no branch key. end