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* 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
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* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
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package org.apache.lucene.codecs.lucene50;
import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.TermVectorsFormat;
import org.apache.lucene.codecs.compressing.CompressingStoredFieldsIndexWriter;
import org.apache.lucene.codecs.compressing.CompressingTermVectorsFormat;
import org.apache.lucene.codecs.compressing.CompressionMode;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.util.packed.BlockPackedWriter;
import org.apache.lucene.util.packed.PackedInts;
/**
* Lucene 5.0 {@link TermVectorsFormat term vectors format}.
* <p>
* Very similarly to {@link Lucene50StoredFieldsFormat}, this format is based
* on compressed chunks of data, with document-level granularity so that a
* document can never span across distinct chunks. Moreover, data is made as
* compact as possible:<ul>
* <li>textual data is compressed using the very light,
* <a href="http://code.google.com/p/lz4/">LZ4</a> compression algorithm,
* <li>binary data is written using fixed-size blocks of
* {@link PackedInts packed ints}.
* </ul>
* <p>
* Term vectors are stored using two files<ul>
* <li>a data file where terms, frequencies, positions, offsets and payloads
* are stored,
* <li>an index file, loaded into memory, used to locate specific documents in
* the data file.
* </ul>
* Looking up term vectors for any document requires at most 1 disk seek.
* <p><b>File formats</b>
* <ol>
* <li><a name="vector_data"></a>
* <p>A vector data file (extension <tt>.tvd</tt>). This file stores terms,
* frequencies, positions, offsets and payloads for every document. Upon writing
* a new segment, it accumulates data into memory until the buffer used to store
* terms and payloads grows beyond 4KB. Then it flushes all metadata, terms
* and positions to disk using <a href="http://code.google.com/p/lz4/">LZ4</a>
* compression for terms and payloads and
* {@link BlockPackedWriter blocks of packed ints} for positions.</p>
* <p>Here is a more detailed description of the field data file format:</p>
* <ul>
* <li>VectorData (.tvd) --> <Header>, PackedIntsVersion, ChunkSize, <Chunk><sup>ChunkCount</sup>, ChunkCount, DirtyChunkCount, Footer</li>
* <li>Header --> {@link CodecUtil#writeIndexHeader IndexHeader}</li>
* <li>PackedIntsVersion --> {@link PackedInts#VERSION_CURRENT} as a {@link DataOutput#writeVInt VInt}</li>
* <li>ChunkSize is the number of bytes of terms to accumulate before flushing, as a {@link DataOutput#writeVInt VInt}</li>
* <li>ChunkCount is not known in advance and is the number of chunks necessary to store all document of the segment</li>
* <li>Chunk --> DocBase, ChunkDocs, < NumFields >, < FieldNums >, < FieldNumOffs >, < Flags >,
* < NumTerms >, < TermLengths >, < TermFreqs >, < Positions >, < StartOffsets >, < Lengths >,
* < PayloadLengths >, < TermAndPayloads ></li>
* <li>DocBase is the ID of the first doc of the chunk as a {@link DataOutput#writeVInt VInt}</li>
* <li>ChunkDocs is the number of documents in the chunk</li>
* <li>NumFields --> DocNumFields<sup>ChunkDocs</sup></li>
* <li>DocNumFields is the number of fields for each doc, written as a {@link DataOutput#writeVInt VInt} if ChunkDocs==1 and as a {@link PackedInts} array otherwise</li>
* <li>FieldNums --> FieldNumDelta<sup>TotalDistincFields</sup>, a delta-encoded list of the sorted unique field numbers present in the chunk</li>
* <li>FieldNumOffs --> FieldNumOff<sup>TotalFields</sup>, as a {@link PackedInts} array</li>
* <li>FieldNumOff is the offset of the field number in FieldNums</li>
* <li>TotalFields is the total number of fields (sum of the values of NumFields)</li>
* <li>Flags --> Bit < FieldFlags ></li>
* <li>Bit is a single bit which when true means that fields have the same options for every document in the chunk</li>
* <li>FieldFlags --> if Bit==1: Flag<sup>TotalDistinctFields</sup> else Flag<sup>TotalFields</sup></li>
* <li>Flag: a 3-bits int where:<ul>
* <li>the first bit means that the field has positions</li>
* <li>the second bit means that the field has offsets</li>
* <li>the third bit means that the field has payloads</li>
* </ul></li>
* <li>NumTerms --> FieldNumTerms<sup>TotalFields</sup></li>
* <li>FieldNumTerms: the number of terms for each field, using {@link BlockPackedWriter blocks of 64 packed ints}</li>
* <li>TermLengths --> PrefixLength<sup>TotalTerms</sup> SuffixLength<sup>TotalTerms</sup></li>
* <li>TotalTerms: total number of terms (sum of NumTerms)</li>
* <li>PrefixLength: 0 for the first term of a field, the common prefix with the previous term otherwise using {@link BlockPackedWriter blocks of 64 packed ints}</li>
* <li>SuffixLength: length of the term minus PrefixLength for every term using {@link BlockPackedWriter blocks of 64 packed ints}</li>
* <li>TermFreqs --> TermFreqMinus1<sup>TotalTerms</sup></li>
* <li>TermFreqMinus1: (frequency - 1) for each term using {@link BlockPackedWriter blocks of 64 packed ints}</li>
* <li>Positions --> PositionDelta<sup>TotalPositions</sup></li>
* <li>TotalPositions is the sum of frequencies of terms of all fields that have positions</li>
* <li>PositionDelta: the absolute position for the first position of a term, and the difference with the previous positions for following positions using {@link BlockPackedWriter blocks of 64 packed ints}</li>
* <li>StartOffsets --> (AvgCharsPerTerm<sup>TotalDistinctFields</sup>) StartOffsetDelta<sup>TotalOffsets</sup></li>
* <li>TotalOffsets is the sum of frequencies of terms of all fields that have offsets</li>
* <li>AvgCharsPerTerm: average number of chars per term, encoded as a float on 4 bytes. They are not present if no field has both positions and offsets enabled.</li>
* <li>StartOffsetDelta: (startOffset - previousStartOffset - AvgCharsPerTerm * PositionDelta). previousStartOffset is 0 for the first offset and AvgCharsPerTerm is 0 if the field has no positions using {@link BlockPackedWriter blocks of 64 packed ints}</li>
* <li>Lengths --> LengthMinusTermLength<sup>TotalOffsets</sup></li>
* <li>LengthMinusTermLength: (endOffset - startOffset - termLength) using {@link BlockPackedWriter blocks of 64 packed ints}</li>
* <li>PayloadLengths --> PayloadLength<sup>TotalPayloads</sup></li>
* <li>TotalPayloads is the sum of frequencies of terms of all fields that have payloads</li>
* <li>PayloadLength is the payload length encoded using {@link BlockPackedWriter blocks of 64 packed ints}</li>
* <li>TermAndPayloads --> LZ4-compressed representation of < FieldTermsAndPayLoads ><sup>TotalFields</sup></li>
* <li>FieldTermsAndPayLoads --> Terms (Payloads)</li>
* <li>Terms: term bytes</li>
* <li>Payloads: payload bytes (if the field has payloads)</li>
* <li>ChunkCount --> the number of chunks in this file</li>
* <li>DirtyChunkCount --> the number of prematurely flushed chunks in this file</li>
* <li>Footer --> {@link CodecUtil#writeFooter CodecFooter}</li>
* </ul>
* </li>
* <li><a name="vector_index"></a>
* <p>An index file (extension <tt>.tvx</tt>).
* <ul>
* <li>VectorIndex (.tvx) --> <Header>, <ChunkIndex>, Footer</li>
* <li>Header --> {@link CodecUtil#writeIndexHeader IndexHeader}</li>
* <li>ChunkIndex: See {@link CompressingStoredFieldsIndexWriter}</li>
* <li>Footer --> {@link CodecUtil#writeFooter CodecFooter}</li>
* </ul>
* </li>
* </ol>
* @lucene.experimental
*/
public final class Lucene50TermVectorsFormat extends CompressingTermVectorsFormat {
/** Sole constructor. */
public Lucene50TermVectorsFormat() {
super("Lucene50TermVectors", "", CompressionMode.FAST, 1 << 12, 1024);
}
}