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.
 

Method Summary

Modifier and Type	Method and Description
void	bufferSkip(int df) Writes the current skip data to the buffers.
long	writeSkip(IndexOutput output) Writes the buffered skip lists to the given output.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

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