org.apache.lucene.codecs

Class MultiLevelSkipListWriter

java.lang.Object

org.apache.lucene.codecs.MultiLevelSkipListWriter

Direct Known Subclasses:

Lucene40SkipListWriter

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 and Description
protected int	numberOfSkipLevels

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	MultiLevelSkipListWriter(int skipInterval, int maxSkipLevels, int df)

Method Summary

Methods

Modifier and Type	Method and Description
void	bufferSkip(int df) Writes the current skip data to the buffers.
protected void	init()
protected void	resetSkip()
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

Constructor Detail

MultiLevelSkipListWriter

protected MultiLevelSkipListWriter(int skipInterval,
                        int maxSkipLevels,
                        int df)

Method Detail

init

protected void init()

resetSkip

protected void resetSkip()

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

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