B+树分裂错误
我想先说一下我要讲的这个作业。我们应该做一棵B+树。我已经完成了大部分工作,但是当我有节点分裂时我遇到了问题。特别是当节点是非叶节点(不包括根节点)并且它分裂时,我会丢失最右边的指针。
例如,如果树是
|3 5|
|1 2| |4| |5 6|
我丢失了指向 |5 6|
的指针。因此,当我搜索这些值时,我找不到它们,或者当我添加一个遵循该路径的值时,我会得到一个空指针异常。
无论如何,我通常只是将我的代码粘贴到这里,但不幸的是,我们在我的学校出现了作弊问题,并且由于该计划即将到期,我确信我的很多同学都在互联网上搜索代码。我最不想发生的事情就是有人抄袭我的代码。
如果有人不介意查看代码,我很乐意将其发送给您查看。它又是用 Java 编写的,而且相当冗长。
提前致谢。
这是代码。在侧面节点上,当我清除偏移量和键时,我使用 int 和 long MAX_VALUE,因此当我排序时,我知道这些清除的值将转到节点的末尾。 Split 类只是我之前的一个愚蠢的想法,我需要修复。它由节点、偏移量和键组成。最初我想我可能需要返回一个不在分割节点中的偏移量和键。然后我意识到这是愚蠢的,我需要返回的只是新节点本身。
public void add (int key, long offset) throws IOException
{
if (root != null) //start search of where to add the book
{
SplitBucket split = add(root, key, offset); //recursive call
if (split != null) //root has split
{
long newRootOffset;
//make new root and have it point to old root and the split node
BookNode newRoot = new BookNode();
newRoot.changeCurrentChildren(1);
newRoot.setChildKey(0, split.key);
newRoot.setChildOffset(0, root.getMyOffset());
newRoot.setChildOffset(1, split.offset);
newRoot.setChildOffset(2,
root.getChildOffset(Constants.childSize -1));
newRoot.setNode(0, root);
newRoot.setNode(1, split.node);
newRoot.setNode(2, root.getNode(Constants.childSize - 1));
io.setBookNode(root.getMyOffset(), root);
newRootOffset = io.insertNewNode(newRoot);
io.setRoot(newRootOffset);
root = newRoot;
}
}
else //empty tree so create root and add
{
long rootOffset = Long.MAX_VALUE;
root = new BookNode();
root.setChildKey(0, key);
root.setChildOffset(0, offset);
root.changeCurrentChildren(1);
root.switchLeaf(true);
rootOffset = io.insertNewNode(root);
io.setRoot(rootOffset);
root.setMyOffset(rootOffset);
}
}
/**
*
* @param current current BookNode
* @param key Isbn to add
* @param offset offset of Book to add
* @return BookNode if a split occurs
* @throws IOException
*/
private SplitBucket add (BookNode current, int key, long offset)
throws IOException
{
if (current.isLeaf()) // at the bottom level
{
//room to add
if (current.getCurrentChildren() < Constants.childSize - 1)
{
//add the offset and key to the end of the node.
//sort the node and rewrite to file
current.setChildOffset(current.getCurrentChildren(), offset);
current.setChildKey(current.getCurrentChildren(), key);
current.changeCurrentChildren(1);
current.sortKeysAndOffsets();
io.setBookNode(current.getMyOffset(), current);
return null;
}
else //not enough room must split
{ //add offset and key to end of node and sort
current.setChildKey(current.getCurrentChildren(), key);
current.setChildOffset(current.getCurrentChildren(), offset);
current.changeCurrentChildren(1);
current.sortKeysAndOffsets();
int start = current.getCurrentChildren() / 2;
long newNodeOffset =Long.MAX_VALUE;
SplitBucket bucket = new SplitBucket();
BookNode newNode = new BookNode();
newNode.switchLeaf(true);
for(int i = start; i < Constants.childSize; i++)
{
//new node will hold the larger split values
newNode.setChildKey(i - start, current.getChildKey(i));
newNode.setChildOffset(i - start, current.getChildOffset(i));
newNode.setNode(i - start, current.getNode(i));
newNode.changeCurrentChildren(1);
current.setChildKey(i, Integer.MAX_VALUE);
current.setChildOffset(i, Long.MAX_VALUE);
current.setNode(i, null);
current.changeCurrentChildren(-1);
}
//since sorted prior to for loop all data
//needs not to be sorted again
newNode.sortKeysAndOffsets();
current.sortKeysAndOffsets();
//Transferring pre-split nodes 'next' pointer to new node
newNode.setChildOffset(Constants.childSize,
current.getChildOffset(Constants.childSize));
newNode.setNode(Constants.childSize,
current.getNode(Constants.childSize));
newNodeOffset = io.insertNewNode(newNode);
newNode.setMyOffset(newNodeOffset);
current.setChildOffset(Constants.childSize, newNodeOffset);
current.setNode(Constants.childSize, newNode);
io.setBookNode(current.getMyOffset(), current);
bucket.key = newNode.getChildKey(0);
bucket.offset = newNode.getMyOffset();
bucket.node = newNode;
return bucket;
}
}
else //not at a leaf
{
int index = 0;
//find pointer index to follow
while (index < current.getCurrentChildren()
&& key >= current.getChildKey(index))
{
index++;
}
//recursive call
SplitBucket bucket = add(current.getNode(index), key, offset);
if(bucket != null) //split occurred
{
//bucket not full so add here
if(current.getCurrentChildren() < Constants.childSize)
{
current.setChildKey(current.getCurrentChildren(), bucket.key);
current.setChildOffset(current.getCurrentChildren(),
bucket.offset);
current.setNode(current.getCurrentChildren(), bucket.node);
current.changeCurrentChildren(1);
current.sortKeysAndOffsets();
io.setBookNode(current.getMyOffset(), current);
bucket = null;
}
else //bucket is full so split
{
int start = current.getCurrentChildren() / 2;
long newNodeOffset = Long.MAX_VALUE;
BookNode newNode = new BookNode();
for(int i = start; i < Constants.childSize; i++)
{
//larger keys go to the new node
newNode.setChildKey(i - start, current.getChildKey(i));
newNode.setChildOffset(i - start,
current.getChildOffset(i));
newNode.setNode(i - start, current.getNode(i));
newNode.changeCurrentChildren(1);
current.setChildKey(i, Integer.MAX_VALUE);
current.setChildOffset(i, Long.MAX_VALUE);
current.setNode(i, null);
current.changeCurrentChildren(-1);
}
if(bucket.key > newNode.getChildKey(0)) //goes in new bucket
{
newNode.setChildKey(newNode.getCurrentChildren(),
bucket.key);
newNode.setChildOffset(newNode.getCurrentChildren(),
bucket.offset);
newNode.setNode(newNode.getCurrentChildren(),
bucket.node);
newNode.changeCurrentChildren(1);
newNode.sortKeysAndOffsets();
}
else //goes in old bucket
{
current.setChildKey(current.getCurrentChildren(),
bucket.key);
current.setChildOffset(current.getCurrentChildren(),
bucket.offset);
current.setNode(current.getCurrentChildren(),
bucket.node);
current.changeCurrentChildren(1);
current.sortKeysAndOffsets();
}
//may not need this line and next
newNode.setChildOffset(newNode.getCurrentChildren(),
current.getChildOffset(Constants.childSize));
newNode.setNode(newNode.getCurrentChildren(),
current.getNode(Constants.childSize));
newNodeOffset = io.insertNewNode(newNode);
newNode.setMyOffset(newNodeOffset);
io.setBookNode(current.getMyOffset(), current);
bucket = new SplitBucket();
//return middle key value of split node
bucket.key = newNode.getChildKey(
newNode.getCurrentChildren() /2);
bucket.offset = newNode.getMyOffset();
bucket.node = newNode;
return bucket;
}
}
}
return null;
}
I want to be up front so I will say this homework that I am about to talk about. We are suppose to do a B+ tree. I've got it most of the way there but I am having a problem when I have a node split. Specifically when the node is a non-leaf (excluding the root) and it splits I am losing my far right pointer.
For example if the tree was
|3 5|
|1 2| |4| |5 6|
I lose the pointer to |5 6|
. So when I search for those values I cannot find them or when I go to add a value that would follow that path I get a null pointer exception.
Anyway I normally would just paste my code here but, unfortunately, we have developed a problem with cheating in my school and since the program is due soon, I am sure a lot of my classmates are scouring the internet for the code. The last thing I want to happen is some jerk rip off my code.
If anyone wouldn't mind looking at the code I will gladly send it to you to check out. Once again it is in Java and is pretty lengthy.
Thanks in advance.
Here is the code. On a side node When I clear offsets and keys I use int and long MAX_VALUE so when I sort I know those cleared values will go to the end of the node. The Split class is just a dumb idea from earlier I need to fix. It consists of a node, offset, and key. Originally I was thinking that I may need to return an offset and key that wasn't in the split node. I then realized that was dumb and all I would ever need to return was the new node itself.
public void add (int key, long offset) throws IOException
{
if (root != null) //start search of where to add the book
{
SplitBucket split = add(root, key, offset); //recursive call
if (split != null) //root has split
{
long newRootOffset;
//make new root and have it point to old root and the split node
BookNode newRoot = new BookNode();
newRoot.changeCurrentChildren(1);
newRoot.setChildKey(0, split.key);
newRoot.setChildOffset(0, root.getMyOffset());
newRoot.setChildOffset(1, split.offset);
newRoot.setChildOffset(2,
root.getChildOffset(Constants.childSize -1));
newRoot.setNode(0, root);
newRoot.setNode(1, split.node);
newRoot.setNode(2, root.getNode(Constants.childSize - 1));
io.setBookNode(root.getMyOffset(), root);
newRootOffset = io.insertNewNode(newRoot);
io.setRoot(newRootOffset);
root = newRoot;
}
}
else //empty tree so create root and add
{
long rootOffset = Long.MAX_VALUE;
root = new BookNode();
root.setChildKey(0, key);
root.setChildOffset(0, offset);
root.changeCurrentChildren(1);
root.switchLeaf(true);
rootOffset = io.insertNewNode(root);
io.setRoot(rootOffset);
root.setMyOffset(rootOffset);
}
}
/**
*
* @param current current BookNode
* @param key Isbn to add
* @param offset offset of Book to add
* @return BookNode if a split occurs
* @throws IOException
*/
private SplitBucket add (BookNode current, int key, long offset)
throws IOException
{
if (current.isLeaf()) // at the bottom level
{
//room to add
if (current.getCurrentChildren() < Constants.childSize - 1)
{
//add the offset and key to the end of the node.
//sort the node and rewrite to file
current.setChildOffset(current.getCurrentChildren(), offset);
current.setChildKey(current.getCurrentChildren(), key);
current.changeCurrentChildren(1);
current.sortKeysAndOffsets();
io.setBookNode(current.getMyOffset(), current);
return null;
}
else //not enough room must split
{ //add offset and key to end of node and sort
current.setChildKey(current.getCurrentChildren(), key);
current.setChildOffset(current.getCurrentChildren(), offset);
current.changeCurrentChildren(1);
current.sortKeysAndOffsets();
int start = current.getCurrentChildren() / 2;
long newNodeOffset =Long.MAX_VALUE;
SplitBucket bucket = new SplitBucket();
BookNode newNode = new BookNode();
newNode.switchLeaf(true);
for(int i = start; i < Constants.childSize; i++)
{
//new node will hold the larger split values
newNode.setChildKey(i - start, current.getChildKey(i));
newNode.setChildOffset(i - start, current.getChildOffset(i));
newNode.setNode(i - start, current.getNode(i));
newNode.changeCurrentChildren(1);
current.setChildKey(i, Integer.MAX_VALUE);
current.setChildOffset(i, Long.MAX_VALUE);
current.setNode(i, null);
current.changeCurrentChildren(-1);
}
//since sorted prior to for loop all data
//needs not to be sorted again
newNode.sortKeysAndOffsets();
current.sortKeysAndOffsets();
//Transferring pre-split nodes 'next' pointer to new node
newNode.setChildOffset(Constants.childSize,
current.getChildOffset(Constants.childSize));
newNode.setNode(Constants.childSize,
current.getNode(Constants.childSize));
newNodeOffset = io.insertNewNode(newNode);
newNode.setMyOffset(newNodeOffset);
current.setChildOffset(Constants.childSize, newNodeOffset);
current.setNode(Constants.childSize, newNode);
io.setBookNode(current.getMyOffset(), current);
bucket.key = newNode.getChildKey(0);
bucket.offset = newNode.getMyOffset();
bucket.node = newNode;
return bucket;
}
}
else //not at a leaf
{
int index = 0;
//find pointer index to follow
while (index < current.getCurrentChildren()
&& key >= current.getChildKey(index))
{
index++;
}
//recursive call
SplitBucket bucket = add(current.getNode(index), key, offset);
if(bucket != null) //split occurred
{
//bucket not full so add here
if(current.getCurrentChildren() < Constants.childSize)
{
current.setChildKey(current.getCurrentChildren(), bucket.key);
current.setChildOffset(current.getCurrentChildren(),
bucket.offset);
current.setNode(current.getCurrentChildren(), bucket.node);
current.changeCurrentChildren(1);
current.sortKeysAndOffsets();
io.setBookNode(current.getMyOffset(), current);
bucket = null;
}
else //bucket is full so split
{
int start = current.getCurrentChildren() / 2;
long newNodeOffset = Long.MAX_VALUE;
BookNode newNode = new BookNode();
for(int i = start; i < Constants.childSize; i++)
{
//larger keys go to the new node
newNode.setChildKey(i - start, current.getChildKey(i));
newNode.setChildOffset(i - start,
current.getChildOffset(i));
newNode.setNode(i - start, current.getNode(i));
newNode.changeCurrentChildren(1);
current.setChildKey(i, Integer.MAX_VALUE);
current.setChildOffset(i, Long.MAX_VALUE);
current.setNode(i, null);
current.changeCurrentChildren(-1);
}
if(bucket.key > newNode.getChildKey(0)) //goes in new bucket
{
newNode.setChildKey(newNode.getCurrentChildren(),
bucket.key);
newNode.setChildOffset(newNode.getCurrentChildren(),
bucket.offset);
newNode.setNode(newNode.getCurrentChildren(),
bucket.node);
newNode.changeCurrentChildren(1);
newNode.sortKeysAndOffsets();
}
else //goes in old bucket
{
current.setChildKey(current.getCurrentChildren(),
bucket.key);
current.setChildOffset(current.getCurrentChildren(),
bucket.offset);
current.setNode(current.getCurrentChildren(),
bucket.node);
current.changeCurrentChildren(1);
current.sortKeysAndOffsets();
}
//may not need this line and next
newNode.setChildOffset(newNode.getCurrentChildren(),
current.getChildOffset(Constants.childSize));
newNode.setNode(newNode.getCurrentChildren(),
current.getNode(Constants.childSize));
newNodeOffset = io.insertNewNode(newNode);
newNode.setMyOffset(newNodeOffset);
io.setBookNode(current.getMyOffset(), current);
bucket = new SplitBucket();
//return middle key value of split node
bucket.key = newNode.getChildKey(
newNode.getCurrentChildren() /2);
bucket.offset = newNode.getMyOffset();
bucket.node = newNode;
return bucket;
}
}
}
return null;
}
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为失败的测试编写一个测试用例或“主要”方法。然后你可以断点&调试这种情况。
将日志记录放入您的代码中,以输出重要/决定性的信息和信息。它正在做的事情——这样你就可以看到哪里出了问题。
不要记录无趣的内容——记录 API 调用、正在创建/更新的节点以及正在创建的节点。正在分割哪些关键范围。记录真正告诉您正在发生的事情。
如果您不喜欢日志记录,可以单步执行并查看日志。调试。它不如使用日志记录来调试和生产那么高效/高效。不过,设计你的代码。
Write a test case, or a 'main' method, for the test that fails. Then you can breakpoint & debug just that situation.
Put logging in your code, to output the important/ decisive information & things it's doing -- so you can see where it's going wrong.
Don't log uninteresting stuff -- log the API calls, which nodes are being created/ updated & which key ranges are being split. Log what really tells you what's going on.
If you don't like logging, you step thru & debug. It's not as efficient/ productive as using logging to debug & engineer your code, though.