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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"/>
<title>Jakarta Lucene - Index File Formats</title>
</head>
<body bgcolor="#ffffff" text="#000000" link="#525D76">
<table border="0" width="100%" cellspacing="0">
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<p><strong>About</strong></p>
<ul>
<li> <a href="./index.html">Overview</a>
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<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#525D76">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Index File Formats"><strong>Index File Formats</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
This document defines the index file formats used
in Lucene version 1.3.
</p>
<p>
Jakarta Lucene is written in Java, but several
efforts are underway to write versions of Lucene in other programming
languages. If these versions are to remain compatible with Jakarta
Lucene, then a language-independent definition of the Lucene index
format is required. This document thus attempts to provide a
complete and independent definition of the Jakarta Lucene 1.3 file
formats.
</p>
<p>
As Lucene's evolves, this document should evolve.
Versions of Lucene in different programming languages should endeavor
to agree on file formats, and generate new versions of this document.
</p>
<p>
Compatibility notes are provided in this document,
describing how file formats have changed from prior versions.
</p>
</blockquote>
</p>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#525D76">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Definitions"><strong>Definitions</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The fundamental concepts in Lucene are index,
document, field and term.
</p>
<p>
An index contains a sequence of documents.
</p>
<ul>
<li>
<p>
A document is a sequence of fields.
</p>
</li>
<li>
<p>
A field is a named sequence of terms.
</p>
</li>
<li>
A term is a string.
</li>
</ul>
<p>
The same string in two different fields is
considered a different term. Thus terms are represented as a pair of
strings, the first naming the field, and the second naming text
within the field.
</p>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Inverted Indexing"><strong>Inverted Indexing</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The index stores statistics about terms in order
to make term-based search more efficient. Lucene's
index falls into the family of indexes known as an <i>inverted
index.</i> This is because it can list, for a term, the documents that contain
it. This is the inverse of the natural relationship, in which
documents list terms.
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Types of Fields"><strong>Types of Fields</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
In Lucene, fields may be <i>stored</i>, in which
case their text is stored in the index literally, in a non-inverted
manner. Fields that are inverted are called <i>indexed</i>. A field
may be both stored and indexed.</p>
<p>The text of a field may be <i>tokenized</i> into terms to be
indexed, or the text of a field may be used literally as a term to be indexed.
Most fields are
tokenized, but sometimes it is useful for certain identifier fields
to be indexed literally.
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Segments"><strong>Segments</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
Lucene indexes may be composed of multiple sub-indexes, or<i>
segments</i>. Each segment is a fully independent index, which could be searched
separately. Indexes evolve by:
</p>
<ol>
<li><p>Creating new segments for newly added documents.</p>
</li>
<li><p>Merging existing segments.</p>
</li>
</ol>
<p>
Searches may involve multiple segments and/or multiple indexes, each
index potentially composed of a set of segments.
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Document Numbers"><strong>Document Numbers</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
Internally, Lucene refers to documents by an integer <i>document
number</i>. The first document added to an index is numbered zero, and each
subsequent document added gets a number one greater than the previous.
</p>
<p>
<br />
</p>
<p>
Note that a document's number may change, so caution should be taken
when storing these numbers outside of Lucene. In particular, numbers may
change in the following situations:
</p>
<ul>
<li>
<p>
The
numbers stored in each segment are unique only within the segment,
and must be converted before they can be used in a larger context.
The standard technique is to allocate each segment a range of
values, based on the range of numbers used in that segment. To
convert a document number from a segment to an external value, the
segment's <i>base</i> document
number is added. To convert an external value back to a
segment-specific value, the segment is identified by the range that
the external value is in, and the segment's base value is
subtracted. For example two five document segments might be
combined, so that the first segment has a base value of zero, and
the second of five. Document three from the second segment would
have an external value of eight.
</p>
</li>
<li>
<p>
When documents are deleted, gaps are created
in the numbering. These are eventually removed as the index evolves
through merging. Deleted documents are dropped when segments are
merged. A freshly-merged segment thus has no gaps in its numbering.
</p>
</li>
</ul>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
</blockquote>
</p>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#525D76">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Overview"><strong>Overview</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
Each segment index maintains the following:
</p>
<ul>
<li><p>Field names. This
contains the set of field names used in the index.
</p>
</li>
<li><p>Stored Field
values. This contains, for each document, a list of attribute-value
pairs, where the attributes are field names. These are used to
store auxiliary information about the document, such as its title,
url, or an identifier to access a
database. The set of stored fields are what is returned for each hit
when searching. This is keyed by document number.
</p>
</li>
<li><p>Term dictionary.
A dictionary containing all of the terms used in all of the indexed
fields of all of the documents. The dictionary also contains the
number of documents which contain the term, and pointers to the
term's frequency and proximity data.
</p>
</li>
<li><p>Term Frequency
data. For each term in the dictionary, the numbers of all the
documents that contain that term, and the frequency of the term in
that document.
</p>
</li>
<li><p>Term Proximity
data. For each term in the dictionary, the positions that the term
occurs in each document.
</p>
</li>
<li><p>Normalization
factors. For each field in each document, a value is stored that is
multiplied into the score for hits on that field.
</p>
</li>
<li><p>Deleted documents.
An optional file indicating which documents are deleted.
</p>
</li>
</ul>
<p>Details on each of these are provided in subsequent sections.
</p>
</blockquote>
</p>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#525D76">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="File Naming"><strong>File Naming</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
All files belonging to a segment have the same name with varying
extensions. The extensions correspond to the different file formats
described below.
</p>
<p>
Typically, all segments
in an index are stored in a single directory, although this is not
required.
</p>
</blockquote>
</p>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#525D76">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Primitive Types"><strong>Primitive Types</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Byte"><strong>Byte</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The most primitive type
is an eight-bit byte. Files are accessed as sequences of bytes. All
other data types are defined as sequences
of bytes, so file formats are byte-order independent.
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="UInt32"><strong>UInt32</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
32-bit unsigned integers are written as four
bytes, high-order bytes first.
</p>
<p>
UInt32 --&gt; &lt;Byte&gt;<sup>4</sup>
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Uint64"><strong>Uint64</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
64-bit unsigned integers are written as eight
bytes, high-order bytes first.
</p>
<p>UInt32 --&gt; &lt;Byte&gt;<sup>8</sup>
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="VInt"><strong>VInt</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
A variable-length format for positive integers is
defined where the high-order bit of each byte indicates whether more
bytes remain to be read. The low-order seven bits are appended as
increasingly more significant bits in the resulting integer value.
Thus values from zero to 127 may be stored in a single byte, values
from 128 to 16,383 may be stored in two bytes, and so on.
</p>
<p><b>VInt Encoding Example</b></p>
<table>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT"><b>Value</b>
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT"><b>First byte</b>
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT"><b>Second byte</b>
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT"><b>Third byte</b>
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">0
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
00000000
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">1
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
00000001
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">2
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
00000010
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">...
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">127
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
01111111
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">128
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
10000000
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm">
00000001
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">129
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
10000001
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm">
00000001
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">130
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
10000010
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm">
00000001
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">...
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">16,383
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
11111111
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm">
01111111
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm"><br />
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">16,384
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
10000000
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm">
10000000
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm">
00000001
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">16,385
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
10000001
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm">
10000000
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm">
00000001
</p>
</font>
</td>
</tr>
<tr>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p align="RIGHT">...
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: 0.11cm; margin-right: 0.01cm">
<br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.07cm; margin-right: 0.01cm">
<br />
</p>
</font>
</td>
<td bgcolor="#a0ddf0" colspan="" rowspan="" valign="top" align="left">
<font color="#000000" size="-1" face="arial,helvetica,sanserif">
<p class="western" align="RIGHT" style="margin-left: -0.47cm; margin-right: 0.01cm">
<br />
</p>
</font>
</td>
</tr>
</table>
<p>
This provides compression while still being
efficient to decode.
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Chars"><strong>Chars</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
Lucene writes unicode
character sequences using the standard UTF-8 encoding.
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="String"><strong>String</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
Lucene writes strings as a VInt representing the length, followed by
the character data.
</p>
<p>
String --&gt; VInt, Chars
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
</blockquote>
</p>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#525D76">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Per-Index Files"><strong>Per-Index Files</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The files in this section exist one-per-index.
</p>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Segments File"><strong>Segments File</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The active segments in the index are stored in the
segment info file. An index only has
a single file in this format, and it is named "segments".
This lists each segment by name, and also contains the size of each
segment.
</p>
<p>
Segments --&gt; SegCount, &lt;SegName, SegSize&gt;<sup>SegCount</sup>
</p>
<p>
SegCount, SegSize --&gt; UInt32
</p>
<p>
SegName --&gt; String
</p>
<p>
SegName is the name of the segment, and is used as the file name prefix
for
all of the files that compose the segment's index.
</p>
<p>
SegSize is the number of documents contained in the segment index.
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Lock Files"><strong>Lock Files</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
Several files are used to indicate that another
process is using an index.
</p>
<ul>
<li>
<p>
When a file named "commit.lock"
is present, a process is currently re-writing the "segments"
file and deleting outdated segment index files, or a process is
reading the "segments"
file and opening the files of the segments it names. This lock file
prevents files from being deleted by another process after a process
has read the "segments"
file but before it has managed to open all of the files of the
segments named therein.
</p>
</li>
<li>
<p>
When a file
named "index.lock"
is present, a process is currently adding documents to an index, or
removing files from that index. This lock file prevents several
processes from attempting to modify an index at the same time.
</p>
</li>
</ul>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Deleteable File"><strong>Deleteable File</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
A file named "deletetable"
contains the names of files that are no longer used by the index, but
which could not be deleted. This is only generated on Win32, where a
file may not be deleted while it is still open.
</p>
<p>
Deleteable --&gt; DelableCount,
&lt;DelableName&gt;<sup>DelableCount</sup>
</p>
<p>DelableCount --&gt; UInt32
</p>
<p>DelableName --&gt;
String
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
</blockquote>
</p>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#525D76">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Per-Segment Files"><strong>Per-Segment Files</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The remaining files are all per-segment, and are
thus defined by suffix.
</p>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Fields"><strong>Fields</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p><br /><b>Field Info</b><br /></p>
<p>
Field names are
stored in the field info file, with suffix .fnm.
</p>
<p>
FieldInfos
(.fnm) --&gt; FieldsCount, &lt;FieldName,
FieldBits&gt;<sup>FieldsCount</sup>
</p>
<p>
FieldsCount --&gt; VInt
</p>
<p>
FieldName --&gt; String
</p>
<p>
FieldBits --&gt; Byte
</p>
<p>
Currently only the low-order bit is used of FieldBits is used. It is
one for
indexed fields, and zero for non-indexed fields.
</p>
<p>
Fields are numbered by their order in this file. Thus field zero is
the
first field in the file, field one the next, and so on. Note that,
like document numbers, field numbers are segment relative.
</p>
<p><br /><b>Stored Fields</b><br /></p>
<p>
Stored fields are represented by two files:
</p>
<ol>
<li>
<p>
The field index, or .fdx file.
</p>
<p>
This contains, for each document, a pointer to
its field data, as follows:
</p>
<p>
FieldIndex
(.fdx) --&gt;
&lt;FieldValuesPosition&gt;<sup>SegSize</sup>
</p>
<p>FieldValuesPosition
--&gt; Uint64
</p>
<p>This
is used to find the location within the field data file of the
fields of a particular document. Because it contains fixed-length
data, this file may be easily randomly accessed. The position of
document<i> n</i>'s<i> </i>field data is the Uint64 at <i>n*8</i> in
this file.
</p>
</li>
<li>
<p>
The field data, or .fdt file.
</p>
<p>
This contains the stored fields of each document,
as follows:
</p>
<p>
FieldData (.fdt) --&gt;
&lt;DocFieldData&gt;<sup>SegSize</sup>
</p>
<p>DocFieldData --&gt;
FieldCount, &lt;FieldNum, Bits, Value&gt;<sup>FieldCount</sup>
</p>
<p>Count --&gt;
VInt
</p>
<p>FieldNum --&gt;
VInt
</p>
<p>Bits --&gt;
Byte
</p>
<p>Value --&gt;
String
</p>
<p>Currently
only the low-order bit is used of Bits is used. It is one for
tokenized fields, and zero for non-tokenized fields.
</p>
</li>
</ol>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Term Dictionary"><strong>Term Dictionary</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The term dictionary is represented as two files:
</p>
<ol>
<li>
<p>
The term infos, or tis file.
</p>
<p>
TermInfoFile (.tis)--&gt;
TermCount, TermInfos
</p>
<p>TermCount --&gt;
UInt32
</p>
<p>TermInfos --&gt;
&lt;TermInfo&gt;<sup>TermCount</sup>
</p>
<p>TermInfo --&gt;
&lt;Term, DocFreq, FreqDelta, ProxDelta&gt;
</p>
<p>Term --&gt;
&lt;PrefixLength, Suffix, FieldNum&gt;
</p>
<p>Suffix --&gt;
String
</p>
<p>PrefixLength,
DocFreq, FreqDelta, ProxDelta<br /> --&gt; VInt
</p>
<p>This
file is sorted by Term. Terms are ordered first lexicographically
by the term's field name, and within that lexicographically by the
term's text.
</p>
<p>Term
text prefixes are shared. The PrefixLength is the number of initial
characters from the previous term which must be pre-pended to a
term's suffix in order to form the term's text. Thus, if the
previous term's text was "bone" and the term is "boy",
the PrefixLength is two and the suffix is "y".
</p>
<p>FieldNumber
determines the term's field, whose name is stored in the .fdt file.
</p>
<p>DocFreq
is the count of documents which contain the term.
</p>
<p>FreqDelta
determines the position of this term's TermFreqs within the .frq
file. In particular, it is the difference between the position of
this term's data in that file and the position of the previous
term's data (or zero, for the first term in the file).
</p>
<p>ProxDelta
determines the position of this term's TermPositions within the .prx
file. In particular, it is the difference between the position of
this term's data in that file and the position of the previous
term's data (or zero, for the first term in the file.
</p>
</li>
<li>
<p>
The term info index, or .tii file.
</p>
<p>
This contains every 128th entry from the .tis
file, along with its location in the "tis" file. This is
designed to be read entirely into memory and used to provide random
access to the "tis" file.
</p>
<p>
The structure of this file is very similar to the
.tis file, with the addition of one item per record, the IndexDelta.
</p>
<p>
TermInfoIndex (.tii)--&gt;
IndexTermCount, TermIndices
</p>
<p>IndexTermCount --&gt;
UInt32
</p>
<p>TermIndices --&gt;
&lt;TermInfo, IndexDelta&gt;<sup>IndexTermCount</sup>
</p>
<p>IndexDelta --&gt;
VInt
</p>
<p>IndexDelta
determines the position of this term's TermInfo the .tis file. In
particular, it is the difference between the position of this term's
entry in that file and the position of the previous term's entry (or
zero for the first term in the file).
</p>
</li>
</ol>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Frequencies"><strong>Frequencies</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The .frq file contains the lists of documents
which contain each term, along with the frequency of the term in that
document.
</p>
<p>FreqFile (.frq) --&gt;
&lt;TermFreqs&gt;<sup>TermCount</sup>
</p>
<p>TermFreqs --&gt;
&lt;TermFreq&gt;<sup>DocFreq</sup>
</p>
<p>TermFreq --&gt;
DocDelta, Freq?
</p>
<p>DocDelta,Freq --&gt;
VInt
</p>
<p>TermFreqs
are ordered by term (the term is implicit, from the .tis file).
</p>
<p>TermFreq
entries are ordered by increasing document number.
</p>
<p>DocDelta
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.
</p>
<p>For
example, the TermFreqs for a term which occurs once in document seven
and three times in document eleven would be the following sequence of
VInts:
</p>
<p> 15,
22, 3
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Positions"><strong>Positions</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>
The .prx file contains the lists of positions that
each term occurs at within documents.
</p>
<p>ProxFile (.prx) --&gt;
&lt;TermPositions&gt;<sup>TermCount</sup>
</p>
<p>TermPositions --&gt;
&lt;Positions&gt;<sup>DocFreq</sup>
</p>
<p>Positions --&gt;
&lt;PositionDelta&gt;<sup>Freq</sup>
</p>
<p>PositionDelta --&gt;
VInt
</p>
<p>TermPositions
are ordered by term (the term is implicit, from the .tis file).
</p>
<p>Positions
entries are ordered by increasing document number (the document
number is implicit from the .frq file).
</p>
<p>PositionDelta
is 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).
</p>
<p>
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:
</p>
<p> 4,
5, 4
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Normalization Factors"><strong>Normalization Factors</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>The .nrm file contains,
for each document, a byte that encodes a value that is multiplied
into the score for hits on that field:
</p>
<p>Norms
(.nrm) --&gt; &lt;Byte&gt;<sup>SegSize</sup>
</p>
<p>Each
byte encodes a floating point value. Bits 0-2 contain the 3-bit
mantissa, and bits 3-8 contain the 5-bit exponent.
</p>
<p>These
are converted to an IEEE single float value as follows:
</p>
<ol>
<li><p>If
the byte is zero, use a zero float.
</p>
</li>
<li><p>Otherwise,
set the sign bit of the float to zero;
</p>
</li>
<li><p>add
48 to the exponent and use this as the float's exponent;
</p>
</li>
<li><p>map
the mantissa to the high-order 3 bits of the float's mantissa; and
</p>
</li>
<li><p>set
the low-order 21 bits of the float's mantissa to zero.
</p>
</li>
</ol>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#828DA6">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Deleted Documents"><strong>Deleted Documents</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>The .del file is
optional, and only exists when a segment contains deletions:
</p>
<p>Deletions
(.del) --&gt; ByteCount,BitCount,Bits
</p>
<p>ByteSize,BitCount --&gt;
Uint32
</p>
<p>Bits --&gt;
&lt;Byte&gt;<sup>ByteCount</sup>
</p>
<p>ByteCount
indicates the number of bytes in Bits. It is typically
(SegSize/8)+1.
</p>
<p>
BitCount
indicates the number of bits that are currently set in Bits.
</p>
<p>Bits
contains one bit for each document indexed. When the bit
corresponding to a document number is set, that document is marked as
deleted. Bit ordering is from least to most significant. Thus, if
Bits contains two bytes, 0x00 and 0x02, then document 9 is marked as
deleted.
</p>
</blockquote>
</td></tr>
<tr><td><br/></td></tr>
</table>
</blockquote>
</p>
</td></tr>
<tr><td><br/></td></tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" width="100%">
<tr><td bgcolor="#525D76">
<font color="#ffffff" face="arial,helvetica,sanserif">
<a name="Limitations"><strong>Limitations</strong></a>
</font>
</td></tr>
<tr><td>
<blockquote>
<p>There
are a few places where these file formats limit the maximum number of
terms and documents to a 32-bit quantity, or to approximately 4
billion. This is not today a problem, but, in the long term,
probably will be. These should therefore be replaced with either
UInt64 values, or better yet, with VInt values which have no limit.
</p>
<p>There
are only two places where the code requires that a value be fixed
size. These are:
</p>
<ol>
<li><p>
The FieldValuesPosition (in the stored field index file, .fdx).
This already uses a UInt64, and so is not a problem.
</p></li>
<li><p>The
TermCount (in the term info file, .tis). This is written last but
is read when the file is first opened, and so is stored at the
front. The indexing code first writes an zero here, then overwrites
it after the rest of the file has been written. So unless this is
stored elsewhere, it must be fixed size and should be changed to a
UInt64.
</p>
</li>
</ol>
<p>Other
than these, all UInt values could be converted to VInt to remove
limitations.
</p>
<p><br /><br />
</p>
</blockquote>
</p>
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