Class BlockTreeTermsWriter

Block-based terms index and dictionary writer.

Writes terms dict and index, block-encoding (column stride) each term's metadata for each set of terms between two index terms.

Files:

Term Dictionary

The .tim file contains the list of terms in each field along with per-term statistics (such as docfreq) and per-term metadata (typically pointers to the postings list for that term in the inverted index).

The .tim is arranged in blocks: with blocks containing a variable number of entries (by default 25-48), where each entry is either a term or a reference to a sub-block.

NOTE: The term dictionary can plug into different postings implementations: the postings writer/reader are actually responsible for encoding and decoding the Postings Metadata and Term Metadata sections.

  • TermsDict (.tim) --> Header, PostingsHeader, NodeBlockNumBlocks, FieldSummary, DirOffset, Footer
  • NodeBlock --> (OuterNode | InnerNode)
  • OuterNode --> EntryCount, SuffixLength, ByteSuffixLength, StatsLength, < TermStats >EntryCount, MetaLength, <TermMetadata>EntryCount
  • InnerNode --> EntryCount, SuffixLength[,Sub?], ByteSuffixLength, StatsLength, < TermStats ? >EntryCount, MetaLength, <TermMetadata ? >EntryCount
  • TermStats --> DocFreq, TotalTermFreq
  • FieldSummary --> NumFields, <FieldNumber, NumTerms, RootCodeLength, ByteRootCodeLength, SumTotalTermFreq?, SumDocFreq, DocCount>NumFields
  • Header --> CodecHeader (WriteHeader(DataOutput, String, Int32)
  • DirOffset --> Uint64 (WriteInt64(Int64))
  • EntryCount,SuffixLength,StatsLength,DocFreq,MetaLength,NumFields, FieldNumber,RootCodeLength,DocCount --> VInt (WriteVInt32(Int32)_
  • TotalTermFreq,NumTerms,SumTotalTermFreq,SumDocFreq --> VLong (WriteVInt64(Int64))
  • Footer --> CodecFooter (WriteFooter(IndexOutput))

Notes:

  • Header is a CodecHeader (WriteHeader(DataOutput, String, Int32)) storing the version information for the BlockTree implementation.
  • DirOffset is a pointer to the FieldSummary section.
  • DocFreq is the count of documents which contain the term.
  • TotalTermFreq is the total number of occurrences of the term. this is encoded as the difference between the total number of occurrences and the DocFreq.
  • FieldNumber is the fields number from Lucene.Net.Codecs.BlockTreeTermsWriter.fieldInfos. (.fnm)
  • NumTerms is the number of unique terms for the field.
  • RootCode points to the root block for the field.
  • SumDocFreq is the total number of postings, the number of term-document pairs across the entire field.
  • DocCount is the number of documents that have at least one posting for this field.
  • PostingsHeader and TermMetadata are plugged into by the specific postings implementation: these contain arbitrary per-file data (such as parameters or versioning information) and per-term data (such as pointers to inverted files).
  • For inner nodes of the tree, every entry will steal one bit to mark whether it points to child nodes(sub-block). If so, the corresponding TermStats and TermMetadata are omitted

Term Index

The .tip file contains an index into the term dictionary, so that it can be accessed randomly. The index is also used to determine when a given term cannot exist on disk (in the .tim file), saving a disk seek.

Notes:

  • The .tip file contains a separate FST for each field. The FST maps a term prefix to the on-disk block that holds all terms starting with that prefix. Each field's IndexStartFP points to its FST.
  • DirOffset is a pointer to the start of the IndexStartFPs for all fields
  • It's possible that an on-disk block would contain too many terms (more than the allowed maximum (default: 48)). When this happens, the block is sub-divided into new blocks (called "floor blocks"), and then the output in the FST for the block's prefix encodes the leading byte of each sub-block, and its file pointer.

This is a Lucene.NET EXPERIMENTAL API, use at your own risk
Inheritance
System.Object
FieldsConsumer
BlockTreeTermsWriter
Implements
System.IDisposable
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.ToString()
Namespace: Lucene.Net.Codecs
Assembly: Lucene.Net.dll
Syntax
public class BlockTreeTermsWriter : FieldsConsumer, IDisposable

Constructors

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BlockTreeTermsWriter(SegmentWriteState, PostingsWriterBase, Int32, Int32)

Create a new writer. The number of items (terms or sub-blocks) per block will aim to be between minItemsInBlock and maxItemsInBlock, though in some cases the blocks may be smaller than the min.

Declaration
public BlockTreeTermsWriter(SegmentWriteState state, PostingsWriterBase postingsWriter, int minItemsInBlock, int maxItemsInBlock)
Parameters
Type Name Description
SegmentWriteState state
PostingsWriterBase postingsWriter
System.Int32 minItemsInBlock
System.Int32 maxItemsInBlock

Fields

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DEFAULT_MAX_BLOCK_SIZE

Suggested default value for the maxItemsInBlock parameter to BlockTreeTermsWriter(SegmentWriteState, PostingsWriterBase, Int32, Int32).

Declaration
public const int DEFAULT_MAX_BLOCK_SIZE = 48
Field Value
Type Description
System.Int32
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DEFAULT_MIN_BLOCK_SIZE

Suggested default value for the minItemsInBlock parameter to BlockTreeTermsWriter(SegmentWriteState, PostingsWriterBase, Int32, Int32).

Declaration
public const int DEFAULT_MIN_BLOCK_SIZE = 25
Field Value
Type Description
System.Int32
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VERSION_APPEND_ONLY

Append-only

Declaration
public const int VERSION_APPEND_ONLY = 1
Field Value
Type Description
System.Int32
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VERSION_CHECKSUM

Checksums.

Declaration
public const int VERSION_CHECKSUM = 3
Field Value
Type Description
System.Int32
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VERSION_CURRENT

Current terms format.

Declaration
public const int VERSION_CURRENT = 3
Field Value
Type Description
System.Int32
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VERSION_META_ARRAY

Meta data as array.

Declaration
public const int VERSION_META_ARRAY = 2
Field Value
Type Description
System.Int32
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VERSION_START

Initial terms format.

Declaration
public const int VERSION_START = 0
Field Value
Type Description
System.Int32

Methods

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AddField(FieldInfo)

Declaration
public override TermsConsumer AddField(FieldInfo field)
Parameters
Type Name Description
FieldInfo field
Returns
Type Description
TermsConsumer
Overrides
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Dispose(Boolean)

Disposes all resources used by this object.

Declaration
protected override void Dispose(bool disposing)
Parameters
Type Name Description
System.Boolean disposing
Overrides
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WriteHeader(IndexOutput)

Writes the terms file header.

Declaration
protected virtual void WriteHeader(IndexOutput out)
Parameters
Type Name Description
IndexOutput out
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WriteIndexHeader(IndexOutput)

Writes the index file header.

Declaration
protected virtual void WriteIndexHeader(IndexOutput out)
Parameters
Type Name Description
IndexOutput out
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WriteIndexTrailer(IndexOutput, Int64)

Writes the index file trailer.

Declaration
protected virtual void WriteIndexTrailer(IndexOutput indexOut, long dirStart)
Parameters
Type Name Description
IndexOutput indexOut
System.Int64 dirStart
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WriteTrailer(IndexOutput, Int64)

Writes the terms file trailer.

Declaration
protected virtual void WriteTrailer(IndexOutput out, long dirStart)
Parameters
Type Name Description
IndexOutput out
System.Int64 dirStart

Implements

System.IDisposable

See Also