/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
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package org.apache.lucene.codecs.lucene84;
import java.io.IOException;
import org.apache.lucene.codecs.BlockTermState;
import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.FieldsConsumer;
import org.apache.lucene.codecs.FieldsProducer;
import org.apache.lucene.codecs.MultiLevelSkipListWriter;
import org.apache.lucene.codecs.PostingsFormat;
import org.apache.lucene.codecs.PostingsReaderBase;
import org.apache.lucene.codecs.PostingsWriterBase;
import org.apache.lucene.codecs.blocktree.BlockTreeTermsReader;
import org.apache.lucene.codecs.blocktree.BlockTreeTermsWriter;
import org.apache.lucene.index.IndexOptions;
import org.apache.lucene.index.SegmentReadState;
import org.apache.lucene.index.SegmentWriteState;
import org.apache.lucene.index.TermState;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.packed.PackedInts;
Lucene 5.0 postings format, which encodes postings in packed integer blocks
for fast decode.
Basic idea:
-
Packed Blocks and VInt Blocks:
In packed blocks, integers are encoded with the same bit width (packed format
): the block size (i.e. number of integers inside block) is fixed (currently 128). Additionally blocks that are all the same value are encoded in an optimized way.
In VInt blocks, integers are encoded as VInt
: the block size is variable.
-
Block structure:
When the postings are long enough, Lucene84PostingsFormat will try to encode most integer data
as a packed block.
Take a term with 259 documents as an example, the first 256 document ids are encoded as two packed
blocks, while the remaining 3 are encoded as one VInt block.
Different kinds of data are always encoded separately into different packed blocks, but may
possibly be interleaved into the same VInt block.
This strategy is applied to pairs:
<document number, frequency>,
<position, payload length>,
<position, offset start, offset length>, and
<position, payload length, offsetstart, offset length>.
-
Skipdata settings:
The structure of skip table is quite similar to previous version of Lucene. Skip interval is the
same as block size, and each skip entry points to the beginning of each block. However, for
the first block, skip data is omitted.
-
Positions, Payloads, and Offsets:
A position is an integer indicating where the term occurs within one document.
A payload is a blob of metadata associated with current position.
An offset is a pair of integers indicating the tokenized start/end offsets for given term
in current position: it is essentially a specialized payload.
When payloads and offsets are not omitted, numPositions==numPayloads==numOffsets (assuming a
null payload contributes one count). As mentioned in block structure, it is possible to encode
these three either combined or separately.
In all cases, payloads and offsets are stored together. When encoded as a packed block,
position data is separated out as .pos, while payloads and offsets are encoded in .pay (payload
metadata will also be stored directly in .pay). When encoded as VInt blocks, all these three are
stored interleaved into the .pos (so is payload metadata).
With this strategy, the majority of payload and offset data will be outside .pos file.
So for queries that require only position data, running on a full index with payloads and offsets,
this reduces disk pre-fetches.
Files and detailed format:
- .tim: Term Dictionary
- .tip: Term Index
- .doc: Frequencies and Skip Data
- .pos: Positions
- .pay: Payloads and Offsets
-
Term Dictionary
The .tim file contains the list of terms in each field along with per-term statistics (such as docfreq) and pointers to the frequencies, positions, payload and skip data in the .doc, .pos, and .pay files. See BlockTreeTermsWriter
for more details on the format.
NOTE: The term dictionary can plug into different postings implementations:
the postings writer/reader are actually responsible for encoding
and decoding the PostingsHeader and TermMetadata sections described here:
- PostingsHeader --> Header, PackedBlockSize
- TermMetadata --> (DocFPDelta|SingletonDocID), PosFPDelta?, PosVIntBlockFPDelta?, PayFPDelta?,
SkipFPDelta?
- Header, -->
IndexHeader
- PackedBlockSize, SingletonDocID -->
VInt
- DocFPDelta, PosFPDelta, PayFPDelta, PosVIntBlockFPDelta, SkipFPDelta -->
VLong
- Footer -->
CodecFooter
Notes:
- Header is a
IndexHeader
storing the version information for the postings.
- PackedBlockSize is the fixed block size for packed blocks. In packed block, bit width is determined by the largest integer. Smaller block size result in smaller variance among width of integers hence smaller indexes. Larger block size result in more efficient bulk i/o hence better acceleration. This value should always be a multiple of 64, currently fixed as 128 as a tradeoff. It is also the skip interval used to accelerate
DocIdSetIterator.advance(int)
. - DocFPDelta determines the position of this term's TermFreqs within the .doc file.
In particular, it is the difference of file offset between this term's
data and previous term's data (or zero, for the first term in the block).On disk it is
stored as the difference from previous value in sequence.
- PosFPDelta determines the position of this term's TermPositions within the .pos file.
While PayFPDelta determines the position of this term's <TermPayloads, TermOffsets?> within
the .pay file. Similar to DocFPDelta, it is the difference between two file positions (or
neglected, for fields that omit payloads and offsets).
- PosVIntBlockFPDelta determines the position of this term's last TermPosition in last pos packed
block within the .pos file. It is synonym for PayVIntBlockFPDelta or OffsetVIntBlockFPDelta.
This is actually used to indicate whether it is necessary to load following
payloads and offsets from .pos instead of .pay. Every time a new block of positions are to be
loaded, the PostingsReader will use this value to check whether current block is packed format
or VInt. When packed format, payloads and offsets are fetched from .pay, otherwise from .pos.
(this value is neglected when total number of positions i.e. totalTermFreq is less or equal
to PackedBlockSize).
- SkipFPDelta determines the position of this term's SkipData within the .doc
file. In particular, it is the length of the TermFreq data.
SkipDelta is only stored if DocFreq is not smaller than SkipMinimum
(i.e. 128 in Lucene84PostingsFormat).
- SingletonDocID is an optimization when a term only appears in one document. In this case, instead
of writing a file pointer to the .doc file (DocFPDelta), and then a VIntBlock at that location, the
single document ID is written to the term dictionary.
-
Term Index
The .tip file contains an index into the term dictionary, so that it can be accessed randomly. See BlockTreeTermsWriter
for more details on the format.
-
Frequencies and Skip Data
The .doc file contains the lists of documents which contain each term, along with the frequency of the term in that document (except when frequencies are omitted: IndexOptions.DOCS
). It also saves skip data to the beginning of each packed or VInt block, when the length of document list is larger than packed block size.
- docFile(.doc) --> Header, <TermFreqs, SkipData?>TermCount, Footer
- Header -->
IndexHeader
- TermFreqs --> <PackedBlock> PackedDocBlockNum,
VIntBlock?
- PackedBlock --> PackedDocDeltaBlock, PackedFreqBlock?
- VIntBlock --> <DocDelta[, Freq?]>DocFreq-PackedBlockSize*PackedDocBlockNum
- SkipData --> <<SkipLevelLength, SkipLevel>
NumSkipLevels-1, SkipLevel>, SkipDatum?
- SkipLevel --> <SkipDatum> TrimmedDocFreq/(PackedBlockSize^(Level + 1))
- SkipDatum --> DocSkip, DocFPSkip, <PosFPSkip, PosBlockOffset, PayLength?,
PayFPSkip?>?, SkipChildLevelPointer?
- PackedDocDeltaBlock, PackedFreqBlock -->
PackedInts
- DocDelta, Freq, DocSkip, DocFPSkip, PosFPSkip, PosBlockOffset, PayByteUpto, PayFPSkip -->
VInt
- SkipChildLevelPointer -->
VLong
- Footer -->
CodecFooter
Notes:
- PackedDocDeltaBlock is theoretically generated from two steps:
- Calculate the difference between each document number and previous one,
and get a d-gaps list (for the first document, use absolute value);
- For those d-gaps from first one to PackedDocBlockNum*PackedBlockSizeth,
separately encode as packed blocks.
If frequencies are not omitted, PackedFreqBlock will be generated without d-gap step.
- VIntBlock stores remaining d-gaps (along with frequencies when possible) with a format
that encodes DocDelta and Freq:
DocDelta: if frequencies are indexed, this determines both the document
number and the frequency. In particular, DocDelta/2 is the difference between
this document number and the previous document number (or zero when this is the
first document in a TermFreqs). When DocDelta is odd, the frequency is one.
When DocDelta is even, the frequency is read as another VInt. If frequencies
are omitted, DocDelta contains the gap (not multiplied by 2) between document
numbers and no frequency information is stored.
For example, the TermFreqs for a term which occurs once in document seven
and three times in document eleven, with frequencies indexed, would be the
following sequence of VInts:
15, 8, 3
If frequencies were omitted (IndexOptions.DOCS
) it would be this sequence of VInts instead:
7,4
- PackedDocBlockNum is the number of packed blocks for current term's docids or frequencies.
In particular, PackedDocBlockNum = floor(DocFreq/PackedBlockSize)
- TrimmedDocFreq = DocFreq % PackedBlockSize == 0 ? DocFreq - 1 : DocFreq. We use this trick since the definition of skip entry is a little different from base interface. In
MultiLevelSkipListWriter
, skip data is assumed to be saved for skipIntervalth, 2*skipIntervalth ... posting in the list. However,
in Lucene84PostingsFormat, the skip data is saved for skipInterval+1th,
2*skipInterval+1th ... posting (skipInterval==PackedBlockSize in this case).
When DocFreq is multiple of PackedBlockSize, MultiLevelSkipListWriter will expect one
more skip data than Lucene84SkipWriter.
- SkipDatum is the metadata of one skip entry.
For the first block (no matter packed or VInt), it is omitted.
- DocSkip records the document number of every PackedBlockSizeth document number in
the postings (i.e. last document number in each packed block). On disk it is stored as the
difference from previous value in the sequence.
- DocFPSkip records the file offsets of each block (excluding )posting at
PackedBlockSize+1th, 2*PackedBlockSize+1th ... , in DocFile.
The file offsets are relative to the start of current term's TermFreqs.
On disk it is also stored as the difference from previous SkipDatum in the sequence.
- Since positions and payloads are also block encoded, the skip should skip to related block first,
then fetch the values according to in-block offset. PosFPSkip and PayFPSkip record the file
offsets of related block in .pos and .pay, respectively. While PosBlockOffset indicates
which value to fetch inside the related block (PayBlockOffset is unnecessary since it is always
equal to PosBlockOffset). Same as DocFPSkip, the file offsets are relative to the start of
current term's TermFreqs, and stored as a difference sequence.
- PayByteUpto indicates the start offset of the current payload. It is equivalent to
the sum of the payload lengths in the current block up to PosBlockOffset
-
Positions
The .pos file contains the lists of positions that each term occurs at within documents. It also
sometimes stores part of payloads and offsets for speedup.
- PosFile(.pos) --> Header, <TermPositions> TermCount, Footer
- Header -->
IndexHeader
- TermPositions --> <PackedPosDeltaBlock> PackedPosBlockNum,
VIntBlock?
- VIntBlock --> <PositionDelta[, PayloadLength?], PayloadData?,
OffsetDelta?, OffsetLength?>PosVIntCount
- PackedPosDeltaBlock -->
PackedInts
- PositionDelta, OffsetDelta, OffsetLength -->
VInt
- PayloadData -->
byte
PayLength
- Footer -->
CodecFooter
Notes:
- TermPositions are order by term (terms are implicit, from the term dictionary), and position
values for each term document pair are incremental, and ordered by document number.
- PackedPosBlockNum is the number of packed blocks for current term's positions, payloads or offsets.
In particular, PackedPosBlockNum = floor(totalTermFreq/PackedBlockSize)
- PosVIntCount is the number of positions encoded as VInt format. In particular,
PosVIntCount = totalTermFreq - PackedPosBlockNum*PackedBlockSize
- The procedure how PackedPosDeltaBlock is generated is the same as PackedDocDeltaBlock
in chapter Frequencies and Skip Data.
- PositionDelta is, if payloads are disabled for the term's field, the
difference between the position of the current occurrence in the document and
the previous occurrence (or zero, if this is the first occurrence in this
document). If payloads are enabled for the term's field, then PositionDelta/2
is the difference between the current and the previous position. If payloads
are enabled and PositionDelta is odd, then PayloadLength is stored, indicating
the length of the payload at the current term position.
- For example, the TermPositions for a term which occurs as the fourth term in
one document, and as the fifth and ninth term in a subsequent document, would
be the following sequence of VInts (payloads disabled):
4, 5, 4
- PayloadData is metadata associated with the current term position. If
PayloadLength is stored at the current position, then it indicates the length
of this payload. If PayloadLength is not stored, then this payload has the same
length as the payload at the previous position.
- OffsetDelta/2 is the difference between this position's startOffset from the previous occurrence (or zero, if this is the first occurrence in this document). If OffsetDelta is odd, then the length (endOffset-startOffset) differs from the previous occurrence and an OffsetLength follows. Offset data is only written for
IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS
.
-
Payloads and Offsets
The .pay file will store payloads and offsets associated with certain term-document positions.
Some payloads and offsets will be separated out into .pos file, for performance reasons.
- PayFile(.pay): --> Header, <TermPayloads, TermOffsets?> TermCount, Footer
- Header -->
IndexHeader
- TermPayloads --> <PackedPayLengthBlock, SumPayLength, PayData> PackedPayBlockNum
- TermOffsets --> <PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock> PackedPayBlockNum
- PackedPayLengthBlock, PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock -->
PackedInts
- SumPayLength -->
VInt
- PayData -->
byte
SumPayLength
- Footer -->
CodecFooter
Notes:
- The order of TermPayloads/TermOffsets will be the same as TermPositions, note that part of
payload/offsets are stored in .pos.
- The procedure how PackedPayLengthBlock and PackedOffsetLengthBlock are generated is the
same as PackedFreqBlock in chapter Frequencies and Skip Data.
While PackedStartDeltaBlock follows a same procedure as PackedDocDeltaBlock.
- PackedPayBlockNum is always equal to PackedPosBlockNum, for the same term. It is also synonym
for PackedOffsetBlockNum.
- SumPayLength is the total length of payloads written within one block, should be the sum
of PayLengths in one packed block.
- PayLength in PackedPayLengthBlock is the length of each payload associated with the current
position.
@lucene.experimental
/**
* Lucene 5.0 postings format, which encodes postings in packed integer blocks
* for fast decode.
*
* <p>
* Basic idea:
* <ul>
* <li>
* <b>Packed Blocks and VInt Blocks</b>:
* <p>In packed blocks, integers are encoded with the same bit width ({@link PackedInts packed format}):
* the block size (i.e. number of integers inside block) is fixed (currently 128). Additionally blocks
* that are all the same value are encoded in an optimized way.</p>
* <p>In VInt blocks, integers are encoded as {@link DataOutput#writeVInt VInt}:
* the block size is variable.</p>
* </li>
*
* <li>
* <b>Block structure</b>:
* <p>When the postings are long enough, Lucene84PostingsFormat will try to encode most integer data
* as a packed block.</p>
* <p>Take a term with 259 documents as an example, the first 256 document ids are encoded as two packed
* blocks, while the remaining 3 are encoded as one VInt block. </p>
* <p>Different kinds of data are always encoded separately into different packed blocks, but may
* possibly be interleaved into the same VInt block. </p>
* <p>This strategy is applied to pairs:
* <document number, frequency>,
* <position, payload length>,
* <position, offset start, offset length>, and
* <position, payload length, offsetstart, offset length>.</p>
* </li>
*
* <li>
* <b>Skipdata settings</b>:
* <p>The structure of skip table is quite similar to previous version of Lucene. Skip interval is the
* same as block size, and each skip entry points to the beginning of each block. However, for
* the first block, skip data is omitted.</p>
* </li>
*
* <li>
* <b>Positions, Payloads, and Offsets</b>:
* <p>A position is an integer indicating where the term occurs within one document.
* A payload is a blob of metadata associated with current position.
* An offset is a pair of integers indicating the tokenized start/end offsets for given term
* in current position: it is essentially a specialized payload. </p>
* <p>When payloads and offsets are not omitted, numPositions==numPayloads==numOffsets (assuming a
* null payload contributes one count). As mentioned in block structure, it is possible to encode
* these three either combined or separately.
* <p>In all cases, payloads and offsets are stored together. When encoded as a packed block,
* position data is separated out as .pos, while payloads and offsets are encoded in .pay (payload
* metadata will also be stored directly in .pay). When encoded as VInt blocks, all these three are
* stored interleaved into the .pos (so is payload metadata).</p>
* <p>With this strategy, the majority of payload and offset data will be outside .pos file.
* So for queries that require only position data, running on a full index with payloads and offsets,
* this reduces disk pre-fetches.</p>
* </li>
* </ul>
*
* <p>
* Files and detailed format:
* <ul>
* <li><tt>.tim</tt>: <a href="#Termdictionary">Term Dictionary</a></li>
* <li><tt>.tip</tt>: <a href="#Termindex">Term Index</a></li>
* <li><tt>.doc</tt>: <a href="#Frequencies">Frequencies and Skip Data</a></li>
* <li><tt>.pos</tt>: <a href="#Positions">Positions</a></li>
* <li><tt>.pay</tt>: <a href="#Payloads">Payloads and Offsets</a></li>
* </ul>
*
* <a name="Termdictionary"></a>
* <dl>
* <dd>
* <b>Term Dictionary</b>
*
* <p>The .tim file contains the list of terms in each
* field along with per-term statistics (such as docfreq)
* and pointers to the frequencies, positions, payload and
* skip data in the .doc, .pos, and .pay files.
* See {@link BlockTreeTermsWriter} for more details on the format.
*
* <p>NOTE: The term dictionary can plug into different postings implementations:
* the postings writer/reader are actually responsible for encoding
* and decoding the PostingsHeader and TermMetadata sections described here:
*
* <ul>
* <li>PostingsHeader --> Header, PackedBlockSize</li>
* <li>TermMetadata --> (DocFPDelta|SingletonDocID), PosFPDelta?, PosVIntBlockFPDelta?, PayFPDelta?,
* SkipFPDelta?</li>
* <li>Header, --> {@link CodecUtil#writeIndexHeader IndexHeader}</li>
* <li>PackedBlockSize, SingletonDocID --> {@link DataOutput#writeVInt VInt}</li>
* <li>DocFPDelta, PosFPDelta, PayFPDelta, PosVIntBlockFPDelta, SkipFPDelta --> {@link DataOutput#writeVLong VLong}</li>
* <li>Footer --> {@link CodecUtil#writeFooter CodecFooter}</li>
* </ul>
* <p>Notes:
* <ul>
* <li>Header is a {@link CodecUtil#writeIndexHeader IndexHeader} storing the version information
* for the postings.</li>
* <li>PackedBlockSize is the fixed block size for packed blocks. In packed block, bit width is
* determined by the largest integer. Smaller block size result in smaller variance among width
* of integers hence smaller indexes. Larger block size result in more efficient bulk i/o hence
* better acceleration. This value should always be a multiple of 64, currently fixed as 128 as
* a tradeoff. It is also the skip interval used to accelerate {@link org.apache.lucene.index.PostingsEnum#advance(int)}.
* <li>DocFPDelta determines the position of this term's TermFreqs within the .doc file.
* In particular, it is the difference of file offset between this term's
* data and previous term's data (or zero, for the first term in the block).On disk it is
* stored as the difference from previous value in sequence. </li>
* <li>PosFPDelta determines the position of this term's TermPositions within the .pos file.
* While PayFPDelta determines the position of this term's <TermPayloads, TermOffsets?> within
* the .pay file. Similar to DocFPDelta, it is the difference between two file positions (or
* neglected, for fields that omit payloads and offsets).</li>
* <li>PosVIntBlockFPDelta determines the position of this term's last TermPosition in last pos packed
* block within the .pos file. It is synonym for PayVIntBlockFPDelta or OffsetVIntBlockFPDelta.
* This is actually used to indicate whether it is necessary to load following
* payloads and offsets from .pos instead of .pay. Every time a new block of positions are to be
* loaded, the PostingsReader will use this value to check whether current block is packed format
* or VInt. When packed format, payloads and offsets are fetched from .pay, otherwise from .pos.
* (this value is neglected when total number of positions i.e. totalTermFreq is less or equal
* to PackedBlockSize).
* <li>SkipFPDelta determines the position of this term's SkipData within the .doc
* file. In particular, it is the length of the TermFreq data.
* SkipDelta is only stored if DocFreq is not smaller than SkipMinimum
* (i.e. 128 in Lucene84PostingsFormat).</li>
* <li>SingletonDocID is an optimization when a term only appears in one document. In this case, instead
* of writing a file pointer to the .doc file (DocFPDelta), and then a VIntBlock at that location, the
* single document ID is written to the term dictionary.</li>
* </ul>
* </dd>
* </dl>
*
* <a name="Termindex"></a>
* <dl>
* <dd>
* <b>Term Index</b>
* <p>The .tip file contains an index into the term dictionary, so that it can be
* accessed randomly. See {@link BlockTreeTermsWriter} for more details on the format.
* </dd>
* </dl>
*
*
* <a name="Frequencies"></a>
* <dl>
* <dd>
* <b>Frequencies and Skip Data</b>
*
* <p>The .doc file contains the lists of documents which contain each term, along
* with the frequency of the term in that document (except when frequencies are
* omitted: {@link IndexOptions#DOCS}). It also saves skip data to the beginning of
* each packed or VInt block, when the length of document list is larger than packed block size.</p>
*
* <ul>
* <li>docFile(.doc) --> Header, <TermFreqs, SkipData?><sup>TermCount</sup>, Footer</li>
* <li>Header --> {@link CodecUtil#writeIndexHeader IndexHeader}</li>
* <li>TermFreqs --> <PackedBlock> <sup>PackedDocBlockNum</sup>,
* VIntBlock? </li>
* <li>PackedBlock --> PackedDocDeltaBlock, PackedFreqBlock?
* <li>VIntBlock --> <DocDelta[, Freq?]><sup>DocFreq-PackedBlockSize*PackedDocBlockNum</sup>
* <li>SkipData --> <<SkipLevelLength, SkipLevel>
* <sup>NumSkipLevels-1</sup>, SkipLevel>, SkipDatum?</li>
* <li>SkipLevel --> <SkipDatum> <sup>TrimmedDocFreq/(PackedBlockSize^(Level + 1))</sup></li>
* <li>SkipDatum --> DocSkip, DocFPSkip, <PosFPSkip, PosBlockOffset, PayLength?,
* PayFPSkip?>?, SkipChildLevelPointer?</li>
* <li>PackedDocDeltaBlock, PackedFreqBlock --> {@link PackedInts PackedInts}</li>
* <li>DocDelta, Freq, DocSkip, DocFPSkip, PosFPSkip, PosBlockOffset, PayByteUpto, PayFPSkip
* -->
* {@link DataOutput#writeVInt VInt}</li>
* <li>SkipChildLevelPointer --> {@link DataOutput#writeVLong VLong}</li>
* <li>Footer --> {@link CodecUtil#writeFooter CodecFooter}</li>
* </ul>
* <p>Notes:
* <ul>
* <li>PackedDocDeltaBlock is theoretically generated from two steps:
* <ol>
* <li>Calculate the difference between each document number and previous one,
* and get a d-gaps list (for the first document, use absolute value); </li>
* <li>For those d-gaps from first one to PackedDocBlockNum*PackedBlockSize<sup>th</sup>,
* separately encode as packed blocks.</li>
* </ol>
* If frequencies are not omitted, PackedFreqBlock will be generated without d-gap step.
* </li>
* <li>VIntBlock stores remaining d-gaps (along with frequencies when possible) with a format
* that encodes DocDelta and Freq:
* <p>DocDelta: if frequencies are indexed, this determines both the document
* number and the frequency. In particular, DocDelta/2 is the difference between
* this document number and the previous document number (or zero when this is the
* first document in a TermFreqs). When DocDelta is odd, the frequency is one.
* When DocDelta is even, the frequency is read as another VInt. If frequencies
* are omitted, DocDelta contains the gap (not multiplied by 2) between document
* numbers and no frequency information is stored.</p>
* <p>For example, the TermFreqs for a term which occurs once in document seven
* and three times in document eleven, with frequencies indexed, would be the
* following sequence of VInts:</p>
* <p>15, 8, 3</p>
* <p>If frequencies were omitted ({@link IndexOptions#DOCS}) it would be this
* sequence of VInts instead:</p>
* <p>7,4</p>
* </li>
* <li>PackedDocBlockNum is the number of packed blocks for current term's docids or frequencies.
* In particular, PackedDocBlockNum = floor(DocFreq/PackedBlockSize) </li>
* <li>TrimmedDocFreq = DocFreq % PackedBlockSize == 0 ? DocFreq - 1 : DocFreq.
* We use this trick since the definition of skip entry is a little different from base interface.
* In {@link MultiLevelSkipListWriter}, skip data is assumed to be saved for
* skipInterval<sup>th</sup>, 2*skipInterval<sup>th</sup> ... posting in the list. However,
* in Lucene84PostingsFormat, the skip data is saved for skipInterval+1<sup>th</sup>,
* 2*skipInterval+1<sup>th</sup> ... posting (skipInterval==PackedBlockSize in this case).
* When DocFreq is multiple of PackedBlockSize, MultiLevelSkipListWriter will expect one
* more skip data than Lucene84SkipWriter. </li>
* <li>SkipDatum is the metadata of one skip entry.
* For the first block (no matter packed or VInt), it is omitted.</li>
* <li>DocSkip records the document number of every PackedBlockSize<sup>th</sup> document number in
* the postings (i.e. last document number in each packed block). On disk it is stored as the
* difference from previous value in the sequence. </li>
* <li>DocFPSkip records the file offsets of each block (excluding )posting at
* PackedBlockSize+1<sup>th</sup>, 2*PackedBlockSize+1<sup>th</sup> ... , in DocFile.
* The file offsets are relative to the start of current term's TermFreqs.
* On disk it is also stored as the difference from previous SkipDatum in the sequence.</li>
* <li>Since positions and payloads are also block encoded, the skip should skip to related block first,
* then fetch the values according to in-block offset. PosFPSkip and PayFPSkip record the file
* offsets of related block in .pos and .pay, respectively. While PosBlockOffset indicates
* which value to fetch inside the related block (PayBlockOffset is unnecessary since it is always
* equal to PosBlockOffset). Same as DocFPSkip, the file offsets are relative to the start of
* current term's TermFreqs, and stored as a difference sequence.</li>
* <li>PayByteUpto indicates the start offset of the current payload. It is equivalent to
* the sum of the payload lengths in the current block up to PosBlockOffset</li>
* </ul>
* </dd>
* </dl>
*
* <a name="Positions"></a>
* <dl>
* <dd>
* <b>Positions</b>
* <p>The .pos file contains the lists of positions that each term occurs at within documents. It also
* sometimes stores part of payloads and offsets for speedup.</p>
* <ul>
* <li>PosFile(.pos) --> Header, <TermPositions> <sup>TermCount</sup>, Footer</li>
* <li>Header --> {@link CodecUtil#writeIndexHeader IndexHeader}</li>
* <li>TermPositions --> <PackedPosDeltaBlock> <sup>PackedPosBlockNum</sup>,
* VIntBlock? </li>
* <li>VIntBlock --> <PositionDelta[, PayloadLength?], PayloadData?,
* OffsetDelta?, OffsetLength?><sup>PosVIntCount</sup>
* <li>PackedPosDeltaBlock --> {@link PackedInts PackedInts}</li>
* <li>PositionDelta, OffsetDelta, OffsetLength -->
* {@link DataOutput#writeVInt VInt}</li>
* <li>PayloadData --> {@link DataOutput#writeByte byte}<sup>PayLength</sup></li>
* <li>Footer --> {@link CodecUtil#writeFooter CodecFooter}</li>
* </ul>
* <p>Notes:
* <ul>
* <li>TermPositions are order by term (terms are implicit, from the term dictionary), and position
* values for each term document pair are incremental, and ordered by document number.</li>
* <li>PackedPosBlockNum is the number of packed blocks for current term's positions, payloads or offsets.
* In particular, PackedPosBlockNum = floor(totalTermFreq/PackedBlockSize) </li>
* <li>PosVIntCount is the number of positions encoded as VInt format. In particular,
* PosVIntCount = totalTermFreq - PackedPosBlockNum*PackedBlockSize</li>
* <li>The procedure how PackedPosDeltaBlock is generated is the same as PackedDocDeltaBlock
* in chapter <a href="#Frequencies">Frequencies and Skip Data</a>.</li>
* <li>PositionDelta is, if payloads are disabled for the term's field, the
* difference between the position of the current occurrence in the document and
* the previous occurrence (or zero, if this is the first occurrence in this
* document). If payloads are enabled for the term's field, then PositionDelta/2
* is the difference between the current and the previous position. If payloads
* are enabled and PositionDelta is odd, then PayloadLength is stored, indicating
* the length of the payload at the current term position.</li>
* <li>For example, the TermPositions for a term which occurs as the fourth term in
* one document, and as the fifth and ninth term in a subsequent document, would
* be the following sequence of VInts (payloads disabled):
* <p>4, 5, 4</p></li>
* <li>PayloadData is metadata associated with the current term position. If
* PayloadLength is stored at the current position, then it indicates the length
* of this payload. If PayloadLength is not stored, then this payload has the same
* length as the payload at the previous position.</li>
* <li>OffsetDelta/2 is the difference between this position's startOffset from the
* previous occurrence (or zero, if this is the first occurrence in this document).
* If OffsetDelta is odd, then the length (endOffset-startOffset) differs from the
* previous occurrence and an OffsetLength follows. Offset data is only written for
* {@link IndexOptions#DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS}.</li>
* </ul>
* </dd>
* </dl>
*
* <a name="Payloads"></a>
* <dl>
* <dd>
* <b>Payloads and Offsets</b>
* <p>The .pay file will store payloads and offsets associated with certain term-document positions.
* Some payloads and offsets will be separated out into .pos file, for performance reasons.
* <ul>
* <li>PayFile(.pay): --> Header, <TermPayloads, TermOffsets?> <sup>TermCount</sup>, Footer</li>
* <li>Header --> {@link CodecUtil#writeIndexHeader IndexHeader}</li>
* <li>TermPayloads --> <PackedPayLengthBlock, SumPayLength, PayData> <sup>PackedPayBlockNum</sup>
* <li>TermOffsets --> <PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock> <sup>PackedPayBlockNum</sup>
* <li>PackedPayLengthBlock, PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock --> {@link PackedInts PackedInts}</li>
* <li>SumPayLength --> {@link DataOutput#writeVInt VInt}</li>
* <li>PayData --> {@link DataOutput#writeByte byte}<sup>SumPayLength</sup></li>
* <li>Footer --> {@link CodecUtil#writeFooter CodecFooter}</li>
* </ul>
* <p>Notes:
* <ul>
* <li>The order of TermPayloads/TermOffsets will be the same as TermPositions, note that part of
* payload/offsets are stored in .pos.</li>
* <li>The procedure how PackedPayLengthBlock and PackedOffsetLengthBlock are generated is the
* same as PackedFreqBlock in chapter <a href="#Frequencies">Frequencies and Skip Data</a>.
* While PackedStartDeltaBlock follows a same procedure as PackedDocDeltaBlock.</li>
* <li>PackedPayBlockNum is always equal to PackedPosBlockNum, for the same term. It is also synonym
* for PackedOffsetBlockNum.</li>
* <li>SumPayLength is the total length of payloads written within one block, should be the sum
* of PayLengths in one packed block.</li>
* <li>PayLength in PackedPayLengthBlock is the length of each payload associated with the current
* position.</li>
* </ul>
* </dd>
* </dl>
*
* @lucene.experimental
*/
public final class Lucene84PostingsFormat extends PostingsFormat {
Filename extension for document number, frequencies, and skip data.
See chapter: Frequencies and Skip Data
/**
* Filename extension for document number, frequencies, and skip data.
* See chapter: <a href="#Frequencies">Frequencies and Skip Data</a>
*/
public static final String DOC_EXTENSION = "doc";
Filename extension for positions.
See chapter: Positions
/**
* Filename extension for positions.
* See chapter: <a href="#Positions">Positions</a>
*/
public static final String POS_EXTENSION = "pos";
Filename extension for payloads and offsets.
See chapter: Payloads and Offsets
/**
* Filename extension for payloads and offsets.
* See chapter: <a href="#Payloads">Payloads and Offsets</a>
*/
public static final String PAY_EXTENSION = "pay";
Size of blocks. /** Size of blocks. */
public static final int BLOCK_SIZE = ForUtil.BLOCK_SIZE;
Expert: The maximum number of skip levels. Smaller values result in
slightly smaller indexes, but slower skipping in big posting lists.
/**
* Expert: The maximum number of skip levels. Smaller values result in
* slightly smaller indexes, but slower skipping in big posting lists.
*/
static final int MAX_SKIP_LEVELS = 10;
final static String TERMS_CODEC = "Lucene84PostingsWriterTerms";
final static String DOC_CODEC = "Lucene84PostingsWriterDoc";
final static String POS_CODEC = "Lucene84PostingsWriterPos";
final static String PAY_CODEC = "Lucene84PostingsWriterPay";
// Increment version to change it
final static int VERSION_START = 0;
// Better compression of the terms dictionary in case most terms have a docFreq of 1
final static int VERSION_COMPRESSED_TERMS_DICT_IDS = 1;
final static int VERSION_CURRENT = VERSION_COMPRESSED_TERMS_DICT_IDS;
private final int minTermBlockSize;
private final int maxTermBlockSize;
Creates Lucene84PostingsFormat
with default settings. /** Creates {@code Lucene84PostingsFormat} with default
* settings. */
public Lucene84PostingsFormat() {
this(BlockTreeTermsWriter.DEFAULT_MIN_BLOCK_SIZE, BlockTreeTermsWriter.DEFAULT_MAX_BLOCK_SIZE);
}
Creates Lucene84PostingsFormat
with custom values for minBlockSize
and
maxBlockSize
passed to block terms dictionary. @see BlockTreeTermsWriter#BlockTreeTermsWriter(SegmentWriteState,PostingsWriterBase,int,int) /** Creates {@code Lucene84PostingsFormat} with custom
* values for {@code minBlockSize} and {@code
* maxBlockSize} passed to block terms dictionary.
* @see BlockTreeTermsWriter#BlockTreeTermsWriter(SegmentWriteState,PostingsWriterBase,int,int) */
public Lucene84PostingsFormat(int minTermBlockSize, int maxTermBlockSize) {
super("Lucene84");
BlockTreeTermsWriter.validateSettings(minTermBlockSize, maxTermBlockSize);
this.minTermBlockSize = minTermBlockSize;
this.maxTermBlockSize = maxTermBlockSize;
}
@Override
public String toString() {
return getName();
}
@Override
public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
PostingsWriterBase postingsWriter = new Lucene84PostingsWriter(state);
boolean success = false;
try {
FieldsConsumer ret = new BlockTreeTermsWriter(state,
postingsWriter,
minTermBlockSize,
maxTermBlockSize);
success = true;
return ret;
} finally {
if (!success) {
IOUtils.closeWhileHandlingException(postingsWriter);
}
}
}
@Override
public FieldsProducer fieldsProducer(SegmentReadState state) throws IOException {
PostingsReaderBase postingsReader = new Lucene84PostingsReader(state);
boolean success = false;
try {
FieldsProducer ret = new BlockTreeTermsReader(postingsReader, state);
success = true;
return ret;
} finally {
if (!success) {
IOUtils.closeWhileHandlingException(postingsReader);
}
}
}
Holds all state required for Lucene84PostingsReader
to produce a PostingsEnum
without re-seeking the terms dict. @lucene.internal
/**
* Holds all state required for {@link Lucene84PostingsReader} to produce a
* {@link org.apache.lucene.index.PostingsEnum} without re-seeking the terms dict.
*
* @lucene.internal
*/
public static final class IntBlockTermState extends BlockTermState {
file pointer to the start of the doc ids enumeration, in Lucene84PostingsFormat.DOC_EXTENSION
file /** file pointer to the start of the doc ids enumeration, in {@link #DOC_EXTENSION} file */
public long docStartFP;
file pointer to the start of the positions enumeration, in Lucene84PostingsFormat.POS_EXTENSION
file /** file pointer to the start of the positions enumeration, in {@link #POS_EXTENSION} file */
public long posStartFP;
file pointer to the start of the payloads enumeration, in Lucene84PostingsFormat.PAY_EXTENSION
file /** file pointer to the start of the payloads enumeration, in {@link #PAY_EXTENSION} file */
public long payStartFP;
file offset for the start of the skip list, relative to docStartFP, if there are more than ForUtil.BLOCK_SIZE
docs; otherwise -1 /** file offset for the start of the skip list, relative to docStartFP, if there are more
* than {@link ForUtil#BLOCK_SIZE} docs; otherwise -1 */
public long skipOffset;
file offset for the last position in the last block, if there are more than ForUtil.BLOCK_SIZE
positions; otherwise -1 /** file offset for the last position in the last block, if there are more than
* {@link ForUtil#BLOCK_SIZE} positions; otherwise -1 */
public long lastPosBlockOffset;
docid when there is a single pulsed posting, otherwise -1.
freq is always implicitly totalTermFreq in this case. /** docid when there is a single pulsed posting, otherwise -1.
* freq is always implicitly totalTermFreq in this case. */
public int singletonDocID;
Sole constructor. /** Sole constructor. */
public IntBlockTermState() {
skipOffset = -1;
lastPosBlockOffset = -1;
singletonDocID = -1;
}
@Override
public IntBlockTermState clone() {
IntBlockTermState other = new IntBlockTermState();
other.copyFrom(this);
return other;
}
@Override
public void copyFrom(TermState _other) {
super.copyFrom(_other);
IntBlockTermState other = (IntBlockTermState) _other;
docStartFP = other.docStartFP;
posStartFP = other.posStartFP;
payStartFP = other.payStartFP;
lastPosBlockOffset = other.lastPosBlockOffset;
skipOffset = other.skipOffset;
singletonDocID = other.singletonDocID;
}
@Override
public String toString() {
return super.toString() + " docStartFP=" + docStartFP + " posStartFP=" + posStartFP + " payStartFP=" + payStartFP + " lastPosBlockOffset=" + lastPosBlockOffset + " singletonDocID=" + singletonDocID;
}
}
}