Package org.apache.lucene.codecs.memory

Class FSTTermsWriter

java.lang.Object

org.apache.lucene.codecs.FieldsConsumer

org.apache.lucene.codecs.memory.FSTTermsWriter

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable

public class FSTTermsWriter
extends FieldsConsumer

FST-based term dict, using metadata as FST output. The FST directly holds the mapping between <term, metadata>. Term metadata consists of three parts: 1. term statistics: docFreq, totalTermFreq; 2. monotonic long[], e.g. the pointer to the postings list for that term; 3. generic byte[], e.g. other information need by postings reader.

File:

• .tst: Term Dictionary

Term Dictionary

The .tst contains a list of FSTs, one for each field. The FST maps a term to its corresponding statistics (e.g. docfreq) and metadata (e.g. information for postings list reader like file pointer to postings list).

Typically the metadata is separated into two parts:

• Monotonical long array: Some metadata will always be ascending in order with the corresponding term. This part is used by FST to share outputs between arcs.
• Generic byte array: Used to store non-monotonic metadata.

File format:

• TermsDict(.tst) --> Header, PostingsHeader, FieldSummary, DirOffset
• FieldSummary --> NumFields, <FieldNumber, NumTerms, SumTotalTermFreq?, SumDocFreq, DocCount, LongsSize, TermFST >^NumFields
• TermFST --> FST<TermData>
• TermData --> Flag, BytesSize?, LongDelta^LongsSize?, Byte^BytesSize?, < DocFreq[Same?], (TotalTermFreq-DocFreq) > ?
• Header --> IndexHeader
• DirOffset --> Uint64
• DocFreq, LongsSize, BytesSize, NumFields, FieldNumber, DocCount --> VInt
• TotalTermFreq, NumTerms, SumTotalTermFreq, SumDocFreq, LongDelta --> VLong

Notes:

• The format of PostingsHeader and generic meta bytes are customized by the specific postings implementation: they contain arbitrary per-file data (such as parameters or versioning information), and per-term data (non-monotonic ones like pulsed postings data).
• The format of TermData is determined by FST, typically monotonic metadata will be dense around shallow arcs, while in deeper arcs only generic bytes and term statistics exist.
• The byte Flag is used to indicate which part of metadata exists on current arc. Specially the monotonic part is omitted when it is an array of 0s.
• Since LongsSize is per-field fixed, it is only written once in field summary.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	FSTTermsWriter.FieldMetaData
(package private) class	FSTTermsWriter.TermsWriter

Field Summary

Fields

Modifier and Type	Field	Description
(package private) FieldInfos	fieldInfos
(package private) java.util.List<FSTTermsWriter.FieldMetaData>	fields
(package private) int	maxDoc
(package private) IndexOutput	out
(package private) PostingsWriterBase	postingsWriter
(package private) static java.lang.String	TERMS_CODEC_NAME
(package private) static java.lang.String	TERMS_EXTENSION
static int	TERMS_VERSION_CURRENT
static int	TERMS_VERSION_START

Constructor Summary

Constructors

Constructor	Description
FSTTermsWriter(SegmentWriteState state, PostingsWriterBase postingsWriter)

Method Summary

Modifier and Type	Method	Description
void	close()
void	write(Fields fields, NormsProducer norms)	Write all fields, terms and postings.
private void	writeTrailer(IndexOutput out, long dirStart)

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

merge

Methods inherited from class java.lang.Object

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

Field Detail

TERMS_EXTENSION

static final java.lang.String TERMS_EXTENSION

See Also:

Constant Field Values

TERMS_CODEC_NAME

static final java.lang.String TERMS_CODEC_NAME

See Also:

Constant Field Values

TERMS_VERSION_START

public static final int TERMS_VERSION_START

See Also:

Constant Field Values

TERMS_VERSION_CURRENT

public static final int TERMS_VERSION_CURRENT

See Also:

Constant Field Values

postingsWriter

final PostingsWriterBase postingsWriter

fieldInfos

final FieldInfos fieldInfos

out

IndexOutput out

maxDoc

final int maxDoc

fields

final java.util.List<FSTTermsWriter.FieldMetaData> fields

Constructor Detail

FSTTermsWriter

public FSTTermsWriter(SegmentWriteState state,
                      PostingsWriterBase postingsWriter)
               throws java.io.IOException

Throws:

java.io.IOException

Method Detail

writeTrailer

private void writeTrailer(IndexOutput out,
                          long dirStart)
                   throws java.io.IOException

Throws:

java.io.IOException

write

public void write(Fields fields,
                  NormsProducer norms)
           throws java.io.IOException

Description copied from class: FieldsConsumer

Write all fields, terms and postings. This the "pull" API, allowing you to iterate more than once over the postings, somewhat analogous to using a DOM API to traverse an XML tree.

Notes:

• You must compute index statistics, including each Term's docFreq and totalTermFreq, as well as the summary sumTotalTermFreq, sumTotalDocFreq and docCount.
• You must skip terms that have no docs and fields that have no terms, even though the provided Fields API will expose them; this typically requires lazily writing the field or term until you've actually seen the first term or document.
• The provided Fields instance is limited: you cannot call any methods that return statistics/counts; you cannot pass a non-null live docs when pulling docs/positions enums.

Specified by:

write in class FieldsConsumer

Throws:

java.io.IOException

close

public void close()
           throws java.io.IOException

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable

Specified by:

close in class FieldsConsumer

Throws:

java.io.IOException