org.apache.lucene.codecs.blocktree

Class BlockTreeTermsReader

java.lang.Object

org.apache.lucene.index.Fields

org.apache.lucene.codecs.FieldsProducer

org.apache.lucene.codecs.blocktree.BlockTreeTermsReader

All Implemented Interfaces:

Closeable, AutoCloseable, Iterable<String>, Accountable

public final 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 its own fixed terms index (ie, it does not support a pluggable terms index implementation).

NOTE: this terms dictionary supports min/maxItemsPerBlock during indexing to control how much memory the terms index uses.

If auto-prefix terms were indexed (see BlockTreeTermsWriter), then the Terms.intersect(org.apache.lucene.util.automaton.CompiledAutomaton, org.apache.lucene.util.BytesRef) implementation here will make use of these terms only if the automaton has a binary sink state, i.e. an accept state which has a transition to itself accepting all byte values. For example, both PrefixQuery and TermRangeQuery pass such automata to Terms.intersect(org.apache.lucene.util.automaton.CompiledAutomaton, org.apache.lucene.util.BytesRef).

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.

Field Summary

Fields

Modifier and Type	Field and Description
static int	VERSION_AUTO_PREFIX_TERMS_REMOVED Auto-prefix terms have been superseded by points.
static int	VERSION_CURRENT Current terms format.
static int	VERSION_START Initial terms format.

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

EMPTY_ARRAY

Constructor Summary

Constructors

Constructor and Description
BlockTreeTermsReader(PostingsReaderBase postingsReader, SegmentReadState state) Sole constructor.

Method Summary

Modifier and Type	Method and Description
void	checkIntegrity() Checks consistency of this reader.
void	close()
Collection<Accountable>	getChildResources() Returns nested resources of this class.
Iterator<String>	iterator() Returns an iterator that will step through all fields names.
long	ramBytesUsed() Return the memory usage of this object in bytes.
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.
String	toString()

Methods inherited from class org.apache.lucene.codecs.FieldsProducer

getMergeInstance

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Field Detail

VERSION_START

public static final int VERSION_START

Initial terms format.

See Also:

Constant Field Values

VERSION_AUTO_PREFIX_TERMS_REMOVED

public static final int VERSION_AUTO_PREFIX_TERMS_REMOVED

Auto-prefix terms have been superseded by points.

See Also:

Constant Field Values

VERSION_CURRENT

public static final int VERSION_CURRENT

Current terms format.

See Also:

Constant Field Values

Constructor Detail

BlockTreeTermsReader

public BlockTreeTermsReader(PostingsReaderBase postingsReader,
                            SegmentReadState state)
                     throws IOException

Sole constructor.

Throws:

IOException

Method Detail

close

public void close()
           throws IOException

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

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 interface: Accountable

Return the memory usage of this object in bytes. Negative values are illegal.

getChildResources

public Collection<Accountable> getChildResources()

Description copied from interface: Accountable

Returns nested resources of this class. The result should be a point-in-time snapshot (to avoid race conditions).

See Also:

Accountables

checkIntegrity

public void checkIntegrity()
                    throws IOException

Description copied from class: FieldsProducer

Checks consistency of this reader.

Note that this may be costly in terms of I/O, e.g. may involve computing a checksum value against large data files.

Specified by:

checkIntegrity in class FieldsProducer

Throws:

IOException

toString

public String toString()

Overrides:

toString in class Object