Package org.apache.lucene.codecs

Class BlockTreeTermsWriter

java.lang.Object

org.apache.lucene.codecs.FieldsConsumer

org.apache.lucene.codecs.BlockTreeTermsWriter

All Implemented Interfaces:

Closeable, AutoCloseable

public class BlockTreeTermsWriter
extends FieldsConsumer

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:

• .tim: Term Dictionary
• .tip: Term Index

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, NodeBlock^NumBlocks, FieldSummary, DirOffset
• NodeBlock --> (OuterNode | InnerNode)
• OuterNode --> EntryCount, SuffixLength, Byte^SuffixLength, StatsLength, < TermStats >^EntryCount, MetaLength, <TermMetadata>^EntryCount
• InnerNode --> EntryCount, SuffixLength[,Sub?], Byte^SuffixLength, StatsLength, < TermStats ? >^EntryCount, MetaLength, <TermMetadata ? >^EntryCount
• TermStats --> DocFreq, TotalTermFreq
• FieldSummary --> NumFields, <FieldNumber, NumTerms, RootCodeLength, Byte^{RootCodeLength}, SumTotalTermFreq?, SumDocFreq, DocCount>^NumFields
• Header --> CodecHeader
• DirOffset --> Uint64
• EntryCount,SuffixLength,StatsLength,DocFreq,MetaLength,NumFields, FieldNumber,RootCodeLength,DocCount --> VInt
• TotalTermFreq,NumTerms,SumTotalTermFreq,SumDocFreq --> VLong

Notes:

• Header is a CodecHeader 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 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.

• TermsIndex (.tip) --> Header, FSTIndex^NumFields <IndexStartFP>^NumFields, DirOffset
• Header --> CodecHeader
• DirOffset --> Uint64
• IndexStartFP --> VLong
• FSTIndex --> FST<byte[]>

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.

See Also:

• BlockTreeTermsReader

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_MAX_BLOCK_SIZE	Suggested default value for the maxItemsInBlock parameter to BlockTreeTermsWriter(SegmentWriteState,PostingsWriterBase,int,int).
static final int	DEFAULT_MIN_BLOCK_SIZE	Suggested default value for the minItemsInBlock parameter to BlockTreeTermsWriter(SegmentWriteState,PostingsWriterBase,int,int).
static final int	TERMS_INDEX_VERSION_APPEND_ONLY	Append-only
static final int	TERMS_INDEX_VERSION_CURRENT	Current index format.
static final int	TERMS_INDEX_VERSION_META_ARRAY	Meta data as array
static final int	TERMS_INDEX_VERSION_START	Initial index format.
static final int	TERMS_VERSION_APPEND_ONLY	Append-only
static final int	TERMS_VERSION_CURRENT	Current terms format.
static final int	TERMS_VERSION_META_ARRAY	Meta data as array
static final int	TERMS_VERSION_START	Initial terms format.

Constructor Summary

Constructors

Constructor	Description
BlockTreeTermsWriter(SegmentWriteState state, PostingsWriterBase postingsWriter, int minItemsInBlock, int maxItemsInBlock)	Create a new writer.

Method Summary

Modifier and Type	Method	Description
TermsConsumer	addField(FieldInfo field)	Add a new field
void	close()	Called when we are done adding everything.
protected void	writeHeader(IndexOutput out)	Writes the terms file header.
protected void	writeIndexHeader(IndexOutput out)	Writes the index file header.
protected void	writeIndexTrailer(IndexOutput indexOut, long dirStart)	Writes the index file trailer.
protected void	writeTrailer(IndexOutput out, long dirStart)	Writes the terms file trailer.

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 Details

DEFAULT_MIN_BLOCK_SIZE

public static final int DEFAULT_MIN_BLOCK_SIZE

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

See Also:

• Constant Field Values

DEFAULT_MAX_BLOCK_SIZE

public static final int DEFAULT_MAX_BLOCK_SIZE

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

See Also:

• Constant Field Values

TERMS_VERSION_START

public static final int TERMS_VERSION_START

Initial terms format.

See Also:

• Constant Field Values

TERMS_VERSION_APPEND_ONLY

public static final int TERMS_VERSION_APPEND_ONLY

Append-only

See Also:

• Constant Field Values

TERMS_VERSION_META_ARRAY

public static final int TERMS_VERSION_META_ARRAY

Meta data as array

See Also:

• Constant Field Values

TERMS_VERSION_CURRENT

public static final int TERMS_VERSION_CURRENT

Current terms format.

See Also:

• Constant Field Values

TERMS_INDEX_VERSION_START

public static final int TERMS_INDEX_VERSION_START

Initial index format.

See Also:

• Constant Field Values

TERMS_INDEX_VERSION_APPEND_ONLY

public static final int TERMS_INDEX_VERSION_APPEND_ONLY

Append-only

See Also:

• Constant Field Values

TERMS_INDEX_VERSION_META_ARRAY

public static final int TERMS_INDEX_VERSION_META_ARRAY

Meta data as array

See Also:

• Constant Field Values

TERMS_INDEX_VERSION_CURRENT

public static final int TERMS_INDEX_VERSION_CURRENT

Current index format.

See Also:

• Constant Field Values

Constructor Details

BlockTreeTermsWriter

public BlockTreeTermsWriter(SegmentWriteState state,
 PostingsWriterBase postingsWriter,
 int minItemsInBlock,
 int maxItemsInBlock)
                     throws IOException

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

Throws:

IOException

Method Details

writeHeader

protected void writeHeader(IndexOutput out)
                    throws IOException

Writes the terms file header.

Throws:

IOException

writeIndexHeader

protected void writeIndexHeader(IndexOutput out)
                         throws IOException

Writes the index file header.

Throws:

IOException

writeTrailer

protected void writeTrailer(IndexOutput out,
 long dirStart)
                     throws IOException

Writes the terms file trailer.

Throws:

IOException

writeIndexTrailer

protected void writeIndexTrailer(IndexOutput indexOut,
 long dirStart)
                          throws IOException

Writes the index file trailer.

Throws:

IOException

addField

public TermsConsumer addField(FieldInfo field)
                       throws IOException

Description copied from class: FieldsConsumer

Add a new field

Specified by:

addField in class FieldsConsumer

Throws:

IOException

close

public void close()
           throws IOException

Description copied from class: FieldsConsumer

Called when we are done adding everything.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Specified by:

close in class FieldsConsumer

Throws:

IOException