org.apache.lucene.codecs
Class MultiLevelSkipListWriter

java.lang.Object
  extended by 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
protected  int numberOfSkipLevels
          number of levels in this skip list
 
Constructor Summary
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
 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
 long writeSkip(IndexOutput output)
          Writes the buffered skip lists to the given output.
protected abstract  void writeSkipData(int level, IndexOutput 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 Detail

numberOfSkipLevels

protected int numberOfSkipLevels
number of levels in this skip list

Constructor Detail

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 Detail

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,
                                      IndexOutput 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


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