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.

  • Method Details

    • 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