Package org.apache.lucene.codecs

# Class MultiLevelSkipListWriter

java.lang.Object
org.apache.lucene.codecs.MultiLevelSkipListWriter

public abstract class MultiLevelSkipListWriter extends Object
This abstract class writes skip lists with multiple levels.

     Example for skipInterval = 3:
                                                         c            (skip level 2)
                     c                 c                 c            (skip level 1)
         x     x     x     x     x     x     x     x     x     x      (skip level 0)
     d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d  (posting list)
         3     6     9     12    15    18    21    24    27    30     (df)

     d - document
     x - skip data
     c - skip data with child pointer

     Skip level i contains every skipInterval-th entry from skip level i-1.
     Therefore the number of entries on level i is: floor(df / ((skipInterval ^ (i + 1))).

     Each skip entry on a level i>0 contains a pointer to the corresponding skip entry in list i-1.
     This guarantees a logarithmic amount of skips to find the target document.

     While this class takes care of writing the different skip levels,
     subclasses must define the actual format of the skip data.

WARNING: This API is experimental and might change in incompatible ways in the next release.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected final int`
  `numberOfSkipLevels`
  number of levels in this skip list

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `MultiLevelSkipListWriter(int skipInterval, int maxSkipLevels, int df)`
  Creates a `MultiLevelSkipListWriter`, where `skipInterval` and `skipMultiplier` are the same.
  `protected`
  `MultiLevelSkipListWriter(int skipInterval, int skipMultiplier, int maxSkipLevels, int df)`
  Creates a `MultiLevelSkipListWriter`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `bufferSkip(int df)`
  Writes the current skip data to the buffers.
  `protected void`
  `init()`
  Allocates internal skip buffers.
  `protected void`
  `resetSkip()`
  Creates new buffers or empties the existing ones
  `protected void`
  `writeChildPointer(long childPointer, DataOutput skipBuffer)`
  Writes the child pointer of a block to the given output.
  `protected void`
  `writeLevelLength(long levelLength, IndexOutput output)`
  Writes the length of a level to the given output.
  `long`
  `writeSkip(IndexOutput output)`
  Writes the buffered skip lists to the given output.
  `protected abstract void`
  `writeSkipData(int level, DataOutput skipBuffer)`
  Subclasses must implement the actual skip data encoding in this method.

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

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

- ## Field Details

  - ### numberOfSkipLevels

    protected final int numberOfSkipLevels
    number of levels in this skip list

- ## Constructor Details

  - ### MultiLevelSkipListWriter

    protected MultiLevelSkipListWriter(int skipInterval, int skipMultiplier, int maxSkipLevels, int df)
    Creates a `MultiLevelSkipListWriter`.

  - ### MultiLevelSkipListWriter

    protected MultiLevelSkipListWriter(int skipInterval, int maxSkipLevels, int df)
    Creates a `MultiLevelSkipListWriter`, where `skipInterval` and `skipMultiplier` are the same.

- ## Method Details

  - ### init

    protected void init()
    Allocates internal skip buffers.

  - ### resetSkip

    protected void resetSkip()
    Creates new buffers or empties the existing ones

  - ### writeSkipData

    protected abstract void writeSkipData(int level, DataOutput skipBuffer) throws IOException
    Subclasses must implement the actual skip data encoding in this method.
    Parameters:
      `level` - the level skip data shall be writing for
      `skipBuffer` - the skip buffer to write to
    Throws:
      `IOException`

  - ### bufferSkip

    public void bufferSkip(int df) throws IOException
    Writes the current skip data to the buffers. The current document frequency determines the max level is skip data is to be written to.
    Parameters:
      `df` - the current document frequency
    Throws:
      `IOException` - If an I/O error occurs

  - ### writeSkip

    public long writeSkip(IndexOutput output) throws IOException
    Writes the buffered skip lists to the given output.
    Parameters:
      `output` - the IndexOutput the skip lists shall be written to
    Returns:
      the pointer the skip list starts
    Throws:
      `IOException`

  - ### writeLevelLength

    protected void writeLevelLength(long levelLength, IndexOutput output) throws IOException
    Writes the length of a level to the given output.
    Parameters:
      `levelLength` - the length of a level
      `output` - the IndexOutput the length shall be written to
    Throws:
      `IOException`

  - ### writeChildPointer

    protected void writeChildPointer(long childPointer, DataOutput skipBuffer) throws IOException
    Writes the child pointer of a block to the given output.
    Parameters:
      `childPointer` - block of higher level point to the lower level
      `skipBuffer` - the skip buffer to write to
    Throws:
      `IOException`