internal BPlusTreeNode SplitChild(int childOffset, BPlusTreeNode originalChild, BPlusTreeNode grandParent)
{
// Split the current node into two nodes:
// a. Left node contains all pointers/keywords to the left of the median
// b. Right node contains all pointers/keywords to the right of the median
// c. Parent node gets median keyword pushed into it
//
// Disk-wise: the originalChild is always written back to its original position.
// the newChild is placed into either an available abandoned node or tacked on the end of the file.
// the parent node is written back to its original position IF IT FITS. Since we're coyping a keyword
// up into the parent node, it may cause it to outgrow its allocated size in the file. If this occurs,
// the call to this.Write() implicitly calls relocate(). relocate() will then either write the parent to
// an abandoned node or tack it onto the end of the file.
_tree.Log("------------ BEGIN Splitting node ------------");
_tree.Log("BEGIN Splitting node parent -> ".PadRight(50) + ToString());
_tree.Log("BEGIN Splitting node child -> ".PadRight(50) + originalChild.ToString());
BPlusTreeNode newChild = BPlusTreeNode.CreateNode(_tree);
newChild.IsLeaf = originalChild.IsLeaf;
newChild.KeywordCount = _tree.Fanout - _tree.MinimumChildren;
// assign items left of median
for (int i = 0; i < newChild.KeywordCount; i++)
{
// Left half of original child already has appropriate values
// However, left half of new child needs data from right half of original child
newChild.ChildrenByteOffsets[i] = originalChild.ChildrenByteOffsets[i + _tree.Median + 1];
newChild.Keywords[i] = originalChild.Keywords[i + _tree.Median + 1];
}
newChild.ChildrenByteOffsets[newChild.KeywordCount] = originalChild.ChildrenByteOffsets[_tree.Fanout];
// adjust the new child's relative info as needed (we always add to the right)
if (originalChild.IsLeaf)
{
// only leaves should track siblings
newChild.LeftSiblingFileOffset = originalChild.FileOffset;
newChild.RightSiblingFileOffset = originalChild.RightSiblingFileOffset;
}
else
{
newChild.LeftSiblingFileOffset = -1;
newChild.RightSiblingFileOffset = -1;
}
// make room in parent for the median values
// (copy all those above the childOffset over one)
for (int i = KeywordCount; i > childOffset; i--)
{
ChildrenByteOffsets[i + 1] = ChildrenByteOffsets[i];
Keywords[i] = Keywords[i - 1];
}
KeywordCount++;
Keywords[childOffset] = originalChild.Keywords[_tree.Median];
// just set byterange that points at our new child to the default for now. we'll assign it the proper value later (once we know the true file offsets)
ChildrenByteOffsets[childOffset + 1] = 0;
// if we're splitting a leaf node, we must copy up the median value.
// if we're splitting an index node, we must simply push it up (i.e. do not leave a copy in the original child)
int startErasingAt = _tree.MinimumChildren;
if (!originalChild.IsLeaf)
{
// index node, erase the keyword (as we essentially want to push it up)
startErasingAt--;
}
// assign items right of median (note this effectively means we copy up the median value, not move it up)
for (int i = startErasingAt; i < _tree.Fanout; i++)
{
// Left half of newChild already has proper values (nulls/defaults)
// However, right half of originalChild still has the values we just copied to the left half of newChild.
// null/default those values.
if (originalChild.IsLeaf || i > startErasingAt)
{
originalChild.ChildrenByteOffsets[i] = 0;
}
originalChild.Keywords[i] = String.Empty;
}
// there's always one more child than keyword...
originalChild.ChildrenByteOffsets[_tree.Fanout] = 0;
originalChild.KeywordCount = startErasingAt;
// determine where to put this new child (in an abandoned node or tack onto end of file)
BPlusAbandonedNode abandonedNode = _tree.GetNextAvailableNodeLocation(newChild);
//newChild._chunkSize = abandonedNode.ByteCount;
newChild.FileOffset = abandonedNode.FileOffset;
newChild.Write(this);
// the original child's right sibling must be updated to point at the new child instead
if (originalChild.RightSiblingFileOffset > 0 && originalChild.IsLeaf)
{
BPlusTreeNode originalRightSibling = BPlusTreeNode.Read(_tree, originalChild.RightSiblingFileOffset, true);
originalRightSibling.LeftSiblingFileOffset = newChild.FileOffset;
originalRightSibling.Write(null);
}
// now that we've written the new child out,
// we know what to set the originalChild's right sibling to...
if (originalChild.IsLeaf)
{
originalChild.RightSiblingFileOffset = newChild.FileOffset;
}
originalChild.Write(this);
// we now know all the offsets we need to update in the parent...
ChildrenByteOffsets[childOffset] = originalChild.FileOffset;
ChildrenByteOffsets[childOffset + 1] = newChild.FileOffset;
// this node may relocate because we're adding a keyword to it.
// if it does, we have to be sure our direct parent knows about it (so it can update its child file offset that points to us)
// hence the "grandParentNode". Write() handles updating things correctly if we give it our parent (which is our children's grandparent) :)
if (Write(grandParent))
{
//Debug.WriteLine("would have missed this before");
}
_tree.Log("END Splitting node parent -> ".PadRight(50) + ToString());
_tree.Log("END Splitting node. original child -> ".PadRight(50) + originalChild.ToString());
_tree.Log("END Splitting node. new child -> ".PadRight(50) + newChild.ToString());
_tree.Log("------------ END Splitting node ------------");
return(newChild);
/*
* newChild <- Allocate-Node()
* leaf[newChild] <- leaf[parent]
* n[newChild] <- t - 1
* for j <- 1 to t - 1
* do keyj[newChild] <- keyj+t[parent]
* if not leaf[parent]
* then for j <- 1 to t
* do cj[newChild] <- cj+t[parent]
* n[parent] <- t - 1
* for j <- n[originalChild] + 1 downto i + 1
* do cj+1[originalChild] <- cj[originalChild]
* ci+1 <- newChild
* for j <- n[originalChild] downto i
* do keyj+1[originalChild] <- keyj[originalChild]
* keyi[originalChild] <- keyt[parent]
* n[originalChild] <- n[originalChild] + 1
* Disk-Write(parent)
* Disk-Write(newChild)
* Disk-Write(originalChild)
*
*/
}
private void relocate(BPlusTreeNode parentNode)
{
// this node has outgrown its allotted space.
// we need to move it to the end of the file and update everybody who points to it
// so have to update the following:
// 1. Parent node's pointer
// 2. Left sibling's pointer
// 3. Right sibling's pointer
// 4. All children's parent pointer (which points at this node)
_tree.Log("------------ BEGIN Relocating node ------------");
_tree.Log("BEGIN Relocating node -> ".PadRight(50) + ToString());
// get an abandoned node (or the end of the file, whichever comes first)
BPlusAbandonedNode abandonedNode = _tree.GetNextAvailableNodeLocation(this);
// mark this node as abandoned in the file (and remove from cache)
_tree.AbandonNode(this);
//if (this.IsRoot) {
// // we're relocating the root.
// _tree.Log("TODO: what to do here, if anything?");
//}
if (!IsLeaf)
{
// only leaf nodes should track left/right siblings.
LeftSiblingFileOffset = -1;
RightSiblingFileOffset = -1;
}
if (LeftSiblingFileOffset > -1)
{
BPlusTreeNode originalLeftSibling = BPlusTreeNode.Read(_tree, this.LeftSiblingFileOffset, true);
originalLeftSibling.RightSiblingFileOffset = originalLeftSibling.IsLeaf ? abandonedNode.FileOffset : -1;
_tree.Log(("Updating left sibling node @ " + originalLeftSibling.FileOffset + " -> ").PadRight(50) + originalLeftSibling.ToString());
originalLeftSibling.Write(null);
}
if (RightSiblingFileOffset > -1)
{
BPlusTreeNode originalRightSibling = BPlusTreeNode.Read(_tree, this.RightSiblingFileOffset, true);
originalRightSibling.LeftSiblingFileOffset = originalRightSibling.IsLeaf ? abandonedNode.FileOffset : -1;
_tree.Log(("Updating right sibling node @ " + originalRightSibling.FileOffset + " -> ").PadRight(50) + originalRightSibling.ToString());
originalRightSibling.Write(null);
}
if (this.IsRoot)
{
// special case! no parent means this is the root node.
// update the int at the very beginning of the file to point at the new root node
_tree.WriteRootNodeOffset(abandonedNode.FileOffset);
}
else
{
if (parentNode != null)
{
for (int i = 0; i < parentNode.KeywordCount + 1; i++)
{
if (parentNode.ChildrenByteOffsets[i] == FileOffset)
{
parentNode.ChildrenByteOffsets[i] = abandonedNode.FileOffset;
_tree.Log(("Updating parent node @ " + parentNode.FileOffset + " -> ").PadRight(50) + parentNode.ToString());
parentNode.Write(null);
// the Root node is cached in the tree object -- udpate it if need be
if (parentNode.IsRoot)
{
_tree.Root = parentNode;
}
break;
}
}
}
}
_tree.Writer.BaseStream.Position = abandonedNode.FileOffset;
FileOffset = abandonedNode.FileOffset;
//_chunkSize = abandonedNode.ByteCount;
_tree.Log("END Relocating node (not written yet) -> ".PadRight(50) + ToString());
_tree.Log("------------ END Relocating node ------------");
}
/// <summary>
/// Returns true if the node was relocated during writing
/// </summary>
/// <returns></returns>
internal bool Write(BPlusTreeNode parent)
{
bool relocated = false;
// NOTE: BPlusTree handles all concurrency / multithreaded issues surrounding writing data -- so none of it is considered here
// Since it requires all other reads and writes to block until this write is done, we do not have to worry about
// the file pointer being repositioned in the middle of a write
// remember the start byte offset for later (note 0 is not a valid position for a node in our particular file, so it's ok to use it as an invalid value)
if (FileOffset < 1)
{
// new node, tack on end of file (or in an abandoned node)
BPlusAbandonedNode abandonedNode = _tree.GetNextAvailableNodeLocation(this);
FileOffset = abandonedNode.FileOffset;
// _chunkSize = abandonedNode.ByteCount;
}
// if a node has never been written it's size will be 0.
// this is also true during a SplitChild write, but since by definition we're splitting a node, it must already have
// at least enough space to store 1/2 of its previous keywords -- so it will never require to be relocated.
if (_nodeSizeOnDisk > 0)
{
// since keywords are dynamic in length and the node must be a specific
// size in the file, we need to check if it will overflow the allotted node size
int newSize = CurrentSize;
if (newSize > _nodeSizeOnDisk)
{
// it grew since we read it. if it's over the default, we have to move it.
if (newSize > _chunkSize && (FileOffset + _chunkSize) < _tree.Writer.BaseStream.Length)
{
// it won't fit -- we have to move it (and we're not at the end of the file already)
relocate(parent);
relocated = true;
}
}
}
_tree.Log("Writing node -> ".PadRight(50) + this.ToString());
_tree.Writer.BaseStream.Position = FileOffset;
_tree.Writer.Write(IsLeaf);
_tree.Writer.Write(KeywordCount);
_tree.Writer.Write(LeftSiblingFileOffset);
_tree.Writer.Write(RightSiblingFileOffset);
// write out all byte offsets first (we always do all regardless of KeywordCount)
for (int i = 0; i <= _tree.Fanout; i++)
{
_tree.Writer.Write(ChildrenByteOffsets[i]);
}
// the keyword portion is the only variable length area there is.
//
for (int i = 0; i < _tree.Fanout; i++)
{
if (String.IsNullOrEmpty(Keywords[i]))
{
_tree.Writer.Write("");
}
else
{
_tree.Writer.Write(Keywords[i]);
}
}
// we also must write filler bytes to fill up to the chunksize
int writtenByteCount = (int)(_tree.Writer.BaseStream.Position - FileOffset);
adjustChunkSize(writtenByteCount);
int fillerByteCount = _chunkSize - writtenByteCount;
if (fillerByteCount > 0)
{
_tree.Writer.BaseStream.Write(new byte[fillerByteCount], 0, fillerByteCount);
}
_nodeSizeOnDisk = (int)(_tree.Writer.BaseStream.Position - FileOffset);
// update the cache as needed
_tree.UpdateNodeCache(this);
return(relocated);
}
// here's the vernacular:
// The _keywords array represents all the keywords in this node.
// The _byteRanges array represents all the file offsets in this node for either (a) a keyword or (b) the data itself.
// a. If it is located in an index node (i.e. non-Leaf), the byte range represents the start/end offsets in the index file (used for traversing to other nodes)
// b. If it is located in a Leaf node, the byte range represents the start/end offsets in the data file (for looking up associated hit(s))
// Think ByteRange = pointer to next node or data, Keyword = item we're searching by
// So we always have 1 more pointer (or byterange, BR) than search item (or keyword, K):
//
// |-------- Node ---------|
// | go pi |
// | / | | | \ |
// | BR1 K1 BR2 K2 BR3 |
// |-----------------------|
/// <summary>
/// Creates a new root node for the tree and makes the original root the first child of the new root.
/// </summary>
/// <param name="tree"></param>
/// <returns></returns>
internal static BPlusTreeNode ReplaceRoot(BPlusTree tree, BPlusTreeNode originalRoot, string keyword, long dataByteOffset)
{
// NOTE: This is a very special case.
// replacing the root involves creating 2 new nodes:
// 1. the new root node
// 2. splitting the existing root node into 2 nodes, one of which is a new one
BPlusTreeNode newRoot = null;
// create a new root node, mark it as not a leaf, put it in exact same spot as original root
newRoot = new BPlusTreeNode {
IsLeaf = false,
_tree = tree,
Keywords = new string[tree.Fanout],
ChildrenByteOffsets = new long[tree.Fanout + 1],
KeywordCount = 0,
FileOffset = -1,
LeftSiblingFileOffset = -1,
RightSiblingFileOffset = -1,
};
tree.Log("------------ BEGIN Replacing root ------------");
tree.Log("BEGIN Replacing root. original node -> ".PadRight(50) + originalRoot.ToString());
tree.Log("BEGIN Replacing root. new node -> ".PadRight(50) + newRoot.ToString());
// add our new root to file, update the root node pointer
BPlusAbandonedNode abandoned = tree.GetNextAvailableNodeLocation(originalRoot);
newRoot.FileOffset = abandoned.FileOffset;
newRoot.Write(null);
tree.WriteRootNodeOffset(newRoot.FileOffset);
// trickle-down insert the new keyword/data
if (!String.IsNullOrEmpty(keyword))
{
// split the original
BPlusTreeNode newChild = newRoot.SplitChild(0, originalRoot, null);
tree.Log("CONTINUE Replacing root. new child node -> ".PadRight(50) + originalRoot.ToString());
if (newRoot.Insert(keyword, dataByteOffset, null))
{
// the new root was relocated during insertion (outgrew its allotted space)
// the insert should take care of it
// re-read it in just in case
newRoot = BPlusTreeNode.Read(tree, newRoot.FileOffset, true);
}
}
else
{
newRoot = BPlusTreeNode.Read(tree, newRoot.FileOffset, true);
}
tree.Log("END Replacing root. original node -> ".PadRight(50) + originalRoot.ToString());
// _tree.Log("END Replacing root. new child node -> ".PadRight(50) + newChild.ToString());
tree.Log("END Replacing root. new root -> ".PadRight(50) + newRoot.ToString());
tree.Log("------------ END Replacing root ------------");
return(newRoot);
}
