在本节中，我将会介绍索引文件sph的生成，从上一节我们得知sph文件保存了Sphinx的索引元信息以及一些索引相关的配置信息

SPH文件生成

先来看代码，其中sph文件的生成是在CSphIndex_VLN::WriteHeader这个函数中:

     bool CSphIndex_VLN::WriteHeader ( const BuildHeader_t & tBuildHeader, CSphWriter & fdInfo ) const
{
    // version
    fdInfo.PutDword ( INDEX_MAGIC_HEADER );
    fdInfo.PutDword ( INDEX_FORMAT_VERSION );
    // bits
    fdInfo.PutDword ( USE_64BIT );
    // docinfo
    fdInfo.PutDword ( m_tSettings.m_eDocinfo );
    // schema
    WriteSchema ( fdInfo, m_tSchema );
    // min doc
    fdInfo.PutOffset ( tBuildHeader.m_uMinDocid ); // was dword in v.1
    if ( m_tSettings.m_eDocinfo==SPH_DOCINFO_INLINE )
        fdInfo.PutBytes ( tBuildHeader.m_pMinRow, m_tSchema.GetRowSize()*sizeof(CSphRowitem) );
    // wordlist checkpoints
    fdInfo.PutOffset ( tBuildHeader.m_iDictCheckpointsOffset );
    fdInfo.PutDword ( tBuildHeader.m_iDictCheckpoints );
    fdInfo.PutByte ( tBuildHeader.m_iInfixCodepointBytes );
    fdInfo.PutDword ( (DWORD)tBuildHeader.m_iInfixBlocksOffset );
    fdInfo.PutDword ( tBuildHeader.m_iInfixBlocksWordsSize );
    // index stats
    fdInfo.PutDword ( (DWORD)tBuildHeader.m_iTotalDocuments ); // FIXME? we don't expect over 4G docs per just 1 local index
    fdInfo.PutOffset ( tBuildHeader.m_iTotalBytes );
    fdInfo.PutDword ( tBuildHeader.m_iTotalDups );
    // index settings
    SaveIndexSettings ( fdInfo, m_tSettings );
    // tokenizer info
    assert ( m_pTokenizer );
    SaveTokenizerSettings ( fdInfo, m_pTokenizer, m_tSettings.m_iEmbeddedLimit );
    // dictionary info
    assert ( m_pDict );
    SaveDictionarySettings ( fdInfo, m_pDict, false, m_tSettings.m_iEmbeddedLimit );
    fdInfo.PutDword ( tBuildHeader.m_uKillListSize );
    fdInfo.PutOffset ( tBuildHeader.m_iMinMaxIndex );
    // field filter info
    SaveFieldFilterSettings ( fdInfo, m_pFieldFilter );
    // average field lengths
    if ( m_tSettings.m_bIndexFieldLens )
        ARRAY_FOREACH ( i, m_tSchema.m_dFields )
            fdInfo.PutOffset ( m_dFieldLens[i] );
    return true;
}

然后按顺序来解释下每一项字段的含义.

• 前两个字段INDEX_MAGIC_HEADER和INDEX_FORMAT_VERSION分别是magic number和索引版本号
• 第三个字段USE_64BIT表示是否使用64位的document和word id(默认是使用).
• 然后是写入docinfo,这个字段也就是配置中的docinfo字段(index block中)
• 接下来将会写入schema，也就是索引的schema信息，比如当前索引的字段名，当前需要建立的属性名等等.

    void WriteSchema ( CSphWriter & fdInfo, const CSphSchema & tSchema )
{
    // schema
    fdInfo.PutDword ( tSchema.m_dFields.GetLength() );
    ARRAY_FOREACH ( i, tSchema.m_dFields )
        WriteSchemaColumn ( fdInfo, tSchema.m_dFields[i] );
    fdInfo.PutDword ( tSchema.GetAttrsCount() );
    for ( int i=0; i<tSchema.GetAttrsCount(); i++ )
        WriteSchemaColumn ( fdInfo, tSchema.GetAttr(i) );
}

• 然后是写入当前索引集的最小doc id(m_uMinDocid)
• 接下来是根据docinfo(也就是属性存储)的配置来选择是否写入行信息(当docinfo为inline的话，表示attribute value 将会存储在spd文件中).
• 然后是写入wordlist的checkpoint.
• 然后是索引的统计信息(m_iTotalDocuments/m_iTotalBytes/m_iTotalDups).
• 接下来是写入对应的索引配置信息

void SaveIndexSettings ( CSphWriter & tWriter, const CSphIndexSettings & tSettings )
{
    tWriter.PutDword ( tSettings.m_iMinPrefixLen );
    tWriter.PutDword ( tSettings.m_iMinInfixLen );
    tWriter.PutDword ( tSettings.m_iMaxSubstringLen );
    tWriter.PutByte ( tSettings.m_bHtmlStrip ? 1 : 0 );
    tWriter.PutString ( tSettings.m_sHtmlIndexAttrs.cstr () );
    tWriter.PutString ( tSettings.m_sHtmlRemoveElements.cstr () );
    tWriter.PutByte ( tSettings.m_bIndexExactWords ? 1 : 0 );
    tWriter.PutDword ( tSettings.m_eHitless );
    tWriter.PutDword ( tSettings.m_eHitFormat );
    tWriter.PutByte ( tSettings.m_bIndexSP );
    tWriter.PutString ( tSettings.m_sZones );
    tWriter.PutDword ( tSettings.m_iBoundaryStep );
    tWriter.PutDword ( tSettings.m_iStopwordStep );
    tWriter.PutDword ( tSettings.m_iOvershortStep );
    tWriter.PutDword ( tSettings.m_iEmbeddedLimit );
    tWriter.PutByte ( tSettings.m_eBigramIndex );
    tWriter.PutString ( tSettings.m_sBigramWords );
    tWriter.PutByte ( tSettings.m_bIndexFieldLens );
    tWriter.PutByte ( tSettings.m_eChineseRLP );
    tWriter.PutString ( tSettings.m_sRLPContext );
    tWriter.PutString ( tSettings.m_sIndexTokenFilter );
}

• 写入对应的tokenizer的配置信息,

void SaveTokenizerSettings ( CSphWriter & tWriter, ISphTokenizer * pTokenizer, int iEmbeddedLimit )
{
    assert ( pTokenizer );
    const CSphTokenizerSettings & tSettings = pTokenizer->GetSettings ();
    tWriter.PutByte ( tSettings.m_iType );
    tWriter.PutString ( tSettings.m_sCaseFolding.cstr () );
    tWriter.PutDword ( tSettings.m_iMinWordLen );
    bool bEmbedSynonyms = pTokenizer->GetSynFileInfo ().m_uSize<=(SphOffset_t)iEmbeddedLimit;
    tWriter.PutByte ( bEmbedSynonyms ? 1 : 0 );
    if ( bEmbedSynonyms )
        pTokenizer->WriteSynonyms ( tWriter );
    tWriter.PutString ( tSettings.m_sSynonymsFile.cstr () );
    WriteFileInfo ( tWriter, pTokenizer->GetSynFileInfo () );
    tWriter.PutString ( tSettings.m_sBoundary.cstr () );
    tWriter.PutString ( tSettings.m_sIgnoreChars.cstr () );
    tWriter.PutDword ( tSettings.m_iNgramLen );
    tWriter.PutString ( tSettings.m_sNgramChars.cstr () );
    tWriter.PutString ( tSettings.m_sBlendChars.cstr () );
    tWriter.PutString ( tSettings.m_sBlendMode.cstr () );
}

• 写入dictionary的配置信息(比如stop word之类).

void SaveDictionarySettings ( CSphWriter & tWriter, CSphDict * pDict, bool bForceWordDict, int iEmbeddedLimit )
{
    assert ( pDict );
    const CSphDictSettings & tSettings = pDict->GetSettings ();
    tWriter.PutString ( tSettings.m_sMorphology.cstr () );
.............................
    bool bEmbedStopwords = uTotalSize<=(SphOffset_t)iEmbeddedLimit;
    tWriter.PutByte ( bEmbedStopwords ? 1 : 0 );
    if ( bEmbedStopwords )
        pDict->WriteStopwords ( tWriter );
    tWriter.PutString ( tSettings.m_sStopwords.cstr () );
    tWriter.PutDword ( dSWFileInfos.GetLength () );
    ARRAY_FOREACH ( i, dSWFileInfos )
    {
        tWriter.PutString ( dSWFileInfos[i].m_sFilename.cstr () );
        WriteFileInfo ( tWriter, dSWFileInfos[i] );
    }
    const CSphVector <CSphSavedFile> & dWFFileInfos = pDict->GetWordformsFileInfos ();
    uTotalSize = 0;
    ARRAY_FOREACH ( i, dWFFileInfos )
        uTotalSize += dWFFileInfos[i].m_uSize;
    bool bEmbedWordforms = uTotalSize<=(SphOffset_t)iEmbeddedLimit;
    tWriter.PutByte ( bEmbedWordforms ? 1 : 0 );
    if ( bEmbedWordforms )
        pDict->WriteWordforms ( tWriter );
    tWriter.PutDword ( dWFFileInfos.GetLength() );
    ARRAY_FOREACH ( i, dWFFileInfos )
    {
        tWriter.PutString ( dWFFileInfos[i].m_sFilename.cstr() );
        WriteFileInfo ( tWriter, dWFFileInfos[i] );
    }
    tWriter.PutDword ( tSettings.m_iMinStemmingLen );
    tWriter.PutByte ( tSettings.m_bWordDict || bForceWordDict );
    tWriter.PutByte ( tSettings.m_bStopwordsUnstemmed );
    tWriter.PutString ( pDict->GetMorphDataFingerprint() );
}

• 然后是写入killlist的size（m_uKillListSize)
• 写入m_iMinMaxIndex，这个选项也就是表示document size.

    CSphFixedVector<CSphRowitem> dMinRow ( tNewSchema.GetRowSize() );
    ...............
    int iNewStride = DOCINFO_IDSIZE + tNewSchema.GetRowSize();
    int64_t iNewMinMaxIndex = m_iDocinfo * iNewStride;
..............................
    tBuildHeader.m_iMinMaxIndex = iNewMinMaxIndex;

• 写入regex相关配置(regexp_filter)

void SaveFieldFilterSettings ( CSphWriter & tWriter, ISphFieldFilter * pFieldFilter )
{
    if ( !pFieldFilter )
    {
        tWriter.PutDword ( 0 );
        return;
    }
    CSphFieldFilterSettings tSettings;
    pFieldFilter->GetSettings ( tSettings );
    tWriter.PutDword ( tSettings.m_dRegexps.GetLength() );
    ARRAY_FOREACH ( i, tSettings.m_dRegexps )
        tWriter.PutString ( tSettings.m_dRegexps[i] );
    tWriter.PutByte(1); // deprecated utf8 flag
}

• 最后是写入对应的schema field长度.