Package org.apache.lucene.codecs.memory
Class FSTTermsWriter
- java.lang.Object
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- org.apache.lucene.codecs.FieldsConsumer
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- org.apache.lucene.codecs.memory.FSTTermsWriter
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- All Implemented Interfaces:
Closeable
,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.
- TermsDict(.tst) --> Header, PostingsHeader, FieldSummary, DirOffset
- FieldSummary --> NumFields, <FieldNumber, NumTerms, SumTotalTermFreq?, SumDocFreq, DocCount, LongsSize, TermFST >NumFields
- TermFST -->
FST<TermData>
- TermData --> Flag, BytesSize?, LongDeltaLongsSize?, ByteBytesSize?, < 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.
- WARNING: This API is experimental and might change in incompatible ways in the next release.
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Field Summary
Fields Modifier and Type Field Description static int
TERMS_VERSION_CURRENT
static int
TERMS_VERSION_START
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Constructor Summary
Constructors Constructor Description FSTTermsWriter(SegmentWriteState state, PostingsWriterBase postingsWriter)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
close()
void
write(Fields fields, NormsProducer norms)
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Methods inherited from class org.apache.lucene.codecs.FieldsConsumer
merge
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Field Detail
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TERMS_VERSION_START
public static final int TERMS_VERSION_START
- See Also:
- Constant Field Values
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TERMS_VERSION_CURRENT
public static final int TERMS_VERSION_CURRENT
- See Also:
- Constant Field Values
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Constructor Detail
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FSTTermsWriter
public FSTTermsWriter(SegmentWriteState state, PostingsWriterBase postingsWriter) throws IOException
- Throws:
IOException
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Method Detail
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write
public void write(Fields fields, NormsProducer norms) throws IOException
- Specified by:
write
in classFieldsConsumer
- Throws:
IOException
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close
public void close() throws IOException
- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Specified by:
close
in classFieldsConsumer
- Throws:
IOException
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