org.apache.cassandra.utils

## Class MerkleTree

- java.lang.Object
- - org.apache.cassandra.utils.MerkleTree

All Implemented Interfaces:
  java.io.Serializable

    public class MerkleTree
    extends java.lang.Object
    implements java.io.Serializable

A MerkleTree implemented as a binary tree. A MerkleTree is a full binary tree that represents a perfect binary tree of depth 'hashdepth'. In a perfect binary tree, each leaf contains a sequentially hashed range, and each inner node contains the binary hash of its two children. In the MerkleTree, many ranges will not be split to the full depth of the perfect binary tree: the leaves of this tree are Leaf objects, which contain the computed values of the nodes that would be below them if the tree were perfect. The hash values of the inner nodes of the MerkleTree are calculated lazily based on their children when the hash of a range is requested with hash(range). Inputs passed to TreeRange.validate should be calculated using a very secure hash, because all hashing internal to the tree is accomplished using XOR. If two MerkleTrees have the same hashdepth, they represent a perfect tree of the same depth, and can always be compared, regardless of size or splits.

See Also:
  Serialized Form

### Nested Class Summary

Nested Classes
`static class` `MerkleTree.MerkleTreeSerializer`
`static class` `MerkleTree.RowHash` Hash value representing a row, to be used to pass hashes to the MerkleTree.
`static class` `MerkleTree.TreeDifference`
`static class` `MerkleTree.TreeRange` The public interface to a range in the tree.
`static class` `MerkleTree.TreeRangeIterator` Returns the leaf (range) of a given tree in increasing order.

### Field Summary

Fields
`static int` `CONSISTENT`
`Range<Token>` `fullRange` The top level range that this MerkleTree covers.
`static int` `FULLY_INCONSISTENT`
`byte` `hashdepth`
`static int` `PARTIALLY_INCONSISTENT`
`static byte` `RECOMMENDED_DEPTH`
`static MerkleTree.MerkleTreeSerializer` `serializer`

### Constructor Summary

Constructors
Constructor and Description
`MerkleTree(IPartitioner partitioner, Range<Token> range, byte hashdepth, long maxsize)`

### Method Summary

All Methods Static Methods Instance Methods Concrete Methods
`static java.util.List<MerkleTree.TreeRange>` `difference(MerkleTree ltree, MerkleTree rtree)`
`MerkleTree.TreeRange` `get(Token t)` For testing purposes.
`byte[]` `hash(Range<Token> range)` Hash the given range in the tree.
`EstimatedHistogram` `histogramOfRowCountPerLeaf()`
`EstimatedHistogram` `histogramOfRowSizePerLeaf()`
`void` `init()` Initializes this tree by splitting it until hashdepth is reached, or until an additional level of splits would violate maxsize.
`void` `invalidate(Token t)` Invalidates the ranges containing the given token.
`MerkleTree.TreeRangeIterator` `invalids()` Returns a lazy iterator of invalid TreeRanges that need to be filled in order to make the given Range valid.
`long` `maxsize()`
`void` `maxsize(long maxsize)`
`IPartitioner` `partitioner()`
`long` `rowCount()`
`long` `size()` The number of distinct ranges contained in this tree.
`boolean` `split(Token t)` Splits the range containing the given token, if no tree limits would be violated.
`java.lang.String` `toString()`

### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

### Field Detail

#### serializer

    public static final MerkleTree.MerkleTreeSerializer serializer

#### RECOMMENDED_DEPTH

    public static final byte RECOMMENDED_DEPTH

See Also:
  Constant Field Values

#### CONSISTENT

    public static final int CONSISTENT

See Also:
  Constant Field Values

#### FULLY_INCONSISTENT

    public static final int FULLY_INCONSISTENT

See Also:
  Constant Field Values

#### PARTIALLY_INCONSISTENT

    public static final int PARTIALLY_INCONSISTENT

See Also:
  Constant Field Values

#### hashdepth

    public final byte hashdepth

#### fullRange

    public final Range<Token> fullRange

The top level range that this MerkleTree covers.

### Constructor Detail

#### MerkleTree

    public MerkleTree(IPartitioner partitioner,
                      Range<Token> range,
                      byte hashdepth,
                      long maxsize)

Parameters:
  `partitioner` - The partitioner in use.
  `range` - the range this tree covers
  `hashdepth` - The maximum depth of the tree. 100/(2^depth) is the % of the key space covered by each subrange of a fully populated tree.
  `maxsize` - The maximum number of subranges in the tree.

### Method Detail

#### init

    public void init()

Initializes this tree by splitting it until hashdepth is reached, or until an additional level of splits would violate maxsize. NB: Replaces all nodes in the tree.

#### partitioner

    public IPartitioner partitioner()

#### size

    public long size()

The number of distinct ranges contained in this tree. This is a reasonable measure of the memory usage of the tree (assuming 'this.order' is significant).

#### maxsize

    public long maxsize()

#### maxsize

    public void maxsize(long maxsize)

#### difference

    public static java.util.List<MerkleTree.TreeRange> difference(MerkleTree ltree,
                                                                  MerkleTree rtree)

Parameters:
  `ltree` - First tree.
  `rtree` - Second tree.
Returns:
  A list of the largest contiguous ranges where the given trees disagree.

#### get

    public MerkleTree.TreeRange get(Token t)

For testing purposes. Gets the smallest range containing the token.

#### invalidate

    public void invalidate(Token t)

Invalidates the ranges containing the given token. Useful for testing.

#### hash

    public byte[] hash(Range<Token> range)

Hash the given range in the tree. The range must have been generated with recursive applications of partitioner.midpoint(). NB: Currently does not support wrapping ranges that do not end with partitioner.getMinimumToken().

Returns:
  Null if any subrange of the range is invalid, or if the exact range cannot be calculated using this tree.

#### split

    public boolean split(Token t)

Splits the range containing the given token, if no tree limits would be violated. If the range would be split to a depth below hashdepth, or if the tree already contains maxsize subranges, this operation will fail.

Returns:
  True if the range was successfully split.

#### invalids

    public MerkleTree.TreeRangeIterator invalids()

Returns a lazy iterator of invalid TreeRanges that need to be filled in order to make the given Range valid.

#### histogramOfRowSizePerLeaf

    public EstimatedHistogram histogramOfRowSizePerLeaf()

#### histogramOfRowCountPerLeaf

    public EstimatedHistogram histogramOfRowCountPerLeaf()

#### rowCount

    public long rowCount()

#### toString

    public java.lang.String toString()

Overrides:
  `toString` in class `java.lang.Object`