org.apache.lucene.codecs
Class BlockTreeTermsReader

java.lang.Object
  org.apache.lucene.index.Fields
      org.apache.lucene.codecs.FieldsProducer
          org.apache.lucene.codecs.BlockTreeTermsReader

All Implemented Interfaces:

Closeable, Iterable<String>

public class BlockTreeTermsReader
extends FieldsProducer

A block-based terms index and dictionary that assigns terms to variable length blocks according to how they share prefixes. The terms index is a prefix trie whose leaves are term blocks. The advantage of this approach is that seekExact is often able to determine a term cannot exist without doing any IO, and intersection with Automata is very fast. Note that this terms dictionary has it's own fixed terms index (ie, it does not support a pluggable terms index implementation).

NOTE: this terms dictionary does not support index divisor when opening an IndexReader. Instead, you can change the min/maxItemsPerBlock during indexing.

The data structure used by this implementation is very similar to a burst trie (http://citeseer.ist.psu.edu/viewdoc/summary?doi=10.1.1.18.3499), but with added logic to break up too-large blocks of all terms sharing a given prefix into smaller ones.

Use CheckIndex with the -verbose option to see summary statistics on the blocks in the dictionary. See BlockTreeTermsWriter.

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

Nested Class Summary

class	BlockTreeTermsReader.FieldReader BlockTree's implementation of Terms.
static class	BlockTreeTermsReader.Stats BlockTree statistics for a single field returned by BlockTreeTermsReader.FieldReader.computeStats().

Field Summary

Fields inherited from class org.apache.lucene.index.Fields

EMPTY_ARRAY

Constructor Summary

BlockTreeTermsReader(Directory dir, FieldInfos fieldInfos, SegmentInfo info, PostingsReaderBase postingsReader, IOContext ioContext, String segmentSuffix, int indexDivisor)
Sole constructor.

Method Summary

void	close()
Iterator<String>	iterator() Returns an iterator that will step through all fields names.
long	ramBytesUsed() Returns approximate RAM bytes used
protected int	readHeader(IndexInput input) Reads terms file header.
protected int	readIndexHeader(IndexInput input) Reads index file header.
protected void	seekDir(IndexInput input, long dirOffset) Seek input to the directory offset.
int	size() Returns the number of fields or -1 if the number of distinct field names is unknown.
Terms	terms(String field) Get the Terms for this field.

Methods inherited from class org.apache.lucene.index.Fields

getUniqueTermCount

Methods inherited from class java.lang.Object

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

Constructor Detail

BlockTreeTermsReader

public BlockTreeTermsReader(Directory dir,
                            FieldInfos fieldInfos,
                            SegmentInfo info,
                            PostingsReaderBase postingsReader,
                            IOContext ioContext,
                            String segmentSuffix,
                            int indexDivisor)
                     throws IOException

Sole constructor.

Throws:

IOException

Method Detail

readHeader

protected int readHeader(IndexInput input)
                  throws IOException

Reads terms file header.

Throws:

IOException

readIndexHeader

protected int readIndexHeader(IndexInput input)
                       throws IOException

Reads index file header.

Throws:

IOException

seekDir

protected void seekDir(IndexInput input,
                       long dirOffset)
                throws IOException

Seek input to the directory offset.

Throws:

IOException

close

public void close()
           throws IOException

Specified by:

close in interface Closeable

Specified by:

close in class FieldsProducer

Throws:

IOException

iterator

public Iterator<String> iterator()

Description copied from class: Fields

Returns an iterator that will step through all fields names. This will not return null.

Specified by:

iterator in interface Iterable<String>

Specified by:

iterator in class Fields

terms

public Terms terms(String field)
            throws IOException

Description copied from class: Fields

Get the Terms for this field. This will return null if the field does not exist.

Specified by:

terms in class Fields

Throws:

IOException

size

public int size()

Description copied from class: Fields

Returns the number of fields or -1 if the number of distinct field names is unknown. If >= 0, Fields.iterator() will return as many field names.

Specified by:

size in class Fields

ramBytesUsed

public long ramBytesUsed()

Description copied from class: FieldsProducer

Returns approximate RAM bytes used

Specified by:

ramBytesUsed in class FieldsProducer