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LUCENE-3892: javadocs 

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/pforcodec_3892@1374591 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Michael McCandless 2012-08-18 14:42:59 +00:00
parent bfcd96c689
commit 573f6a734c
2 changed files with 55 additions and 36 deletions
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66
lucene/core/src/java/org/apache/lucene/codecs/block/BlockPostingsFormat.java
View File

@ -1,5 +1,6 @@
package org.apache.lucene.codecs.block;
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
@ -80,7 +81,7 @@ import org.apache.lucene.util.packed.PackedInts;
*
* <li>
* <b>Positions, Payloads, and Offsets</b>:
* <p>A position is an integer indicating where the term occured in one document.
* <p>A position is an integer indicating where the term occurs at 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. </p>
@ -91,6 +92,9 @@ import org.apache.lucene.util.packed.PackedInts;
* 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 block, all these three are
* stored in .pos (so as 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>
@ -119,10 +123,10 @@ import org.apache.lucene.util.packed.PackedInts;
* <li>TermDictionary(.tim) --&gt; Header, DirOffset, PostingsHeader, PackedBlockSize,
* &lt;Block&gt;<sup>NumBlocks</sup>, FieldSummary</li>
* <li>Block --&gt; SuffixBlock, StatsBlock, MetadataBlock</li>
* <li>SuffixBlock --&gt; EntryCount, SuffixLength, Byte<sup>SuffixLength</sup></li>
* <li>SuffixBlock --&gt; EntryCount, SuffixLength, {@link DataOutput#writeByte byte}<sup>SuffixLength</sup></li>
* <li>StatsBlock --&gt; StatsLength, &lt;DocFreq, TotalTermFreq&gt;<sup>EntryCount</sup></li>
* <li>MetadataBlock --&gt; MetaLength, &lt;DocFPDelta,
* &lt;PosFPDelta, PosBlockFPDelta?, PayFPDelta?&gt;?,
* &lt;PosFPDelta, PosVIntBlockFPDelta?, PayFPDelta?&gt;?,
* SkipFPDelta?&gt;<sup>EntryCount</sup></li>
* <li>FieldSummary --&gt; NumFields, &lt;FieldNumber, NumTerms, RootCodeLength,
* Byte<sup>RootCodeLength</sup>, SumDocFreq, DocCount&gt;
@ -130,7 +134,7 @@ import org.apache.lucene.util.packed.PackedInts;
* <li>Header, PostingsHeader --&gt; {@link CodecUtil#writeHeader CodecHeader}</li>
* <li>DirOffset --&gt; {@link DataOutput#writeLong Uint64}</li>
* <li>PackedBlockSize, EntryCount, SuffixLength, StatsLength, DocFreq, MetaLength,
* PosBlockFPDelta, SkipFPDelta, NumFields, FieldNumber, RootCodeLength, DocCount --&gt;
* PosVIntBlockFPDelta , SkipFPDelta, NumFields, FieldNumber, RootCodeLength, DocCount --&gt;
* {@link DataOutput#writeVInt VInt}</li>
* <li>TotalTermFreq, DocFPDelta, PosFPDelta, NumTerms, SumTotalTermFreq, SumDocFreq --&gt;
* {@link DataOutput#writeVLong VLong}</li>
@ -141,27 +145,30 @@ import org.apache.lucene.util.packed.PackedInts;
* <!--NOTE: change this manual html link, when directory structure is changed. -->
* <a href="../../../../../org/apache/lucene/codecs/lucene40/Lucene40PostingsFormat.html#Termdictionary">Lucene40PostingsFormat:TermDictionary</a>
* </li>
* <li>PackedBlockSize is fixed block size for packed blocks. In packed block, bit width is
* <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 accerlerate {@link DocsEnum#advance(int)}.
* a tradeoff. It is also the skip interval used to accelerate {@link DocsEnum#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).</li>
* <li>PayFPDelta determines the position of this term's payload or offset data within the .pay file.
* Similar to DocFPDelta, it is the difference between two file positions (or neglected,
* for fields that omit payloads and offsets, or for the first term in the block).</li>
* <!--TODO: not quite sure, what is the difference?-->
* <li>PosFPDelta and PosBlockFPDelta determine the position of this term's TermPositions within
* the .pos file.
* <li>PosBlockFPDelta determines the position of this term's TermPositions within the .pos file.
* Similar to DocFPDelta, it is the difference between two file positions (or neglected,
* for fields that omit position data, or for the first term in the block).</li>
* 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 &lt;TermPayloads, TermOffsets?&gt; 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. Everytime 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 number of bytes after TermFreqs that the
* SkipData starts. In other words, it is the length of the TermFreq data.
* SkipDelta is only stored if DocFreq is not smaller than SkipMinimum,
* file. In particular, it is the length of the TermFreq data.
* SkipDelta is only stored if DocFreq is not smaller than SkipMinimum
* (i.e. 8 in BlockPostingsFormat).</li>
* </ul>
* </dd>
@ -201,7 +208,8 @@ import org.apache.lucene.util.packed.PackedInts;
* <li>SkipDatum --&gt; DocSkip, DocFPSkip, &lt;PosFPSkip, PosBlockOffset, PayLength?,
* OffsetStart?, PayFPSkip?&gt;?, SkipChildLevelPointer?</li>
* <li>PackedDocDeltaBlock, PackedFreqBlock --&gt; {@link PackedInts PackedInts}</li>
* <li>DocDelta,Freq,DocSkip,DocFPSkip,PosFPSkip,PosBlockOffset,PayLength,OffsetStart,PayFPSkip --&gt;
* <li>DocDelta, Freq, DocSkip, DocFPSkip, PosFPSkip, PosBlockOffset, PayLength, OffsetStart, PayFPSkip
* --&gt;
* {@link DataOutput#writeVInt VInt}</li>
* <li>SkipChildLevelPointer --&gt; {@link DataOutput#writeVLong VLong}</li>
* </ul>
@ -256,8 +264,10 @@ import org.apache.lucene.util.packed.PackedInts;
* <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>Pos(.prx) --&gt; Header, &lt;TermPositions&gt; <sup>TermCount</sup></li>
* <li>Pos(.pos) --&gt; Header, &lt;TermPositions&gt; <sup>TermCount</sup></li>
* <li>Header --&gt; {@link CodecUtil#writeHeader CodecHeader}</li>
* <li>TermPositions --&gt; &lt;PackedPosDeltaBlock&gt; <sup>PackedPosBlockNum</sup>,
* VIntBlock? </li>
@ -272,6 +282,8 @@ import org.apache.lucene.util.packed.PackedInts;
* <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, PackedDocBlockNum = floor(totalTermFreq/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>PosDelta is the same as the format mentioned in
@ -290,10 +302,12 @@ import org.apache.lucene.util.packed.PackedInts;
* <dl>
* <dd>
* <b>Payloads and Offsets</b>
* <p>The .pay file will store payload and offset associated with certain term-document positons.
* Some payloads and offsets will be seperated out into .pos file, for speedup reason.</p>
* <ul>
* <li>PayFile(.pay): --&gt; Header, &lt;TermPayloads, TermOffsets?&gt; <sup>TermCount</sup></li>
* <li>Header --&gt; {@link CodecUtil#writeHeader CodecHeader}</li>
* <li>TermPayloads --&gt; &lt; PackedPayLengthBlock, PayBlockLength, PayData, PackedOffsetStartDeltaBlock?, PackedOffsetLengthBlock &gt; <sup>PackedPayBlockNum</sup>
* <li>TermPayloads --&gt; &lt;PackedPayLengthBlock, PayBlockLength, PayData, PackedOffsetStartDeltaBlock?, PackedOffsetLengthBlock?&gt; <sup>PackedPayBlockNum</sup>
* <li>PackedPayLengthBlock, PackedOffsetStartDeltaBlock, PackedOffsetLengthBlock --&gt; {@link PackedInts PackedInts}</li>
* <li>PayBlockLength --&gt; {@link DataOutput#writeVInt VInt}</li>
* <li>PayData --&gt; {@link DataOutput#writeByte byte}<sup>PayBlockLength</sup></li>
@ -302,11 +316,13 @@ import org.apache.lucene.util.packed.PackedInts;
* <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 is generated is the same as PackedFreqBlock
* in chapter <a href="#Frequencies">Frequencies and Skip Data</a>.</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>PayBlockLength is the total length of payloads written within one block, should be the sum
* of PayLengths in one packed block.</li>
* <li>PayLength is the length of each payload, associated with current position.</li>
* <li>PayLength in PackedPayLengthBlock is the length of each payload, associated with current
* position.</li>
* </u>
* </dd>
* </dl>

3
lucene/core/src/java/org/apache/lucene/codecs/block/BlockPostingsWriter.java
View File

@ -403,8 +403,11 @@ final class BlockPostingsWriter extends PostingsWriterBase {
// }
// }
// totalTermFreq is just total number of positions(or payloads, or offsets)
// associated with current term.
assert stats.totalTermFreq != -1;
if (stats.totalTermFreq > BLOCK_SIZE) {
// record file offset for last pos in last block
lastPosBlockOffset = (int) (posOut.getFilePointer() - posTermStartFP);
} else {
lastPosBlockOffset = -1;