关于使用Filter降低Lucene tf idf打分计算的调研

将query改成filter,lucene中有个QueryWrapperFilter性能比较差，所以基本上都须要自己写filter。包含TermFilter,ExactPhraseFilter,ConjunctionFilter,DisjunctionFilter。

这几天验证下来，还是or改善最明显，4个termfilter,4508个返回结果,在我本机上性能提高1/3。ExactPhraseFilter也有小幅提升(5%-10%)。

最令人不解的是and,原来以为跟结果数和子查询数相关，但几次測试基本都是下降。

附ExactPhraseFilter和ut代码:

import java.io.IOException;
import java.util.ArrayList;

import org.apache.lucene.index.AtomicReaderContext;
import org.apache.lucene.index.DocsAndPositionsEnum;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermContext;
import org.apache.lucene.index.TermState;
import org.apache.lucene.index.Terms;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.search.DocIdSet;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.Filter;
import org.apache.lucene.util.ArrayUtil;
import org.apache.lucene.util.Bits;

// A fake to lucene phrase query, but far simplified.
public class ExactPhraseFilter extends Filter {
    protected final ArrayList<Term> terms = new ArrayList<Term>();
    protected final ArrayList<Integer> positions = new ArrayList<Integer>();
    
    protected String fieldName;
    
    public void add(Term term) {
        if (terms.size() == 0) {
            fieldName = term.field();
        } else {
            assert fieldName == term.field();
        }
        positions.add(Integer.valueOf(terms.size()));
        terms.add(term);
    }
    
    @Override
    public DocIdSet getDocIdSet(AtomicReaderContext context, Bits acceptDocs) throws IOException
    {
        return new ExactPhraseDocIdSet(context, acceptDocs);
    }
    
    static class PostingAndFreq implements Comparable<PostingAndFreq> {
        DocsAndPositionsEnum posEnum;
        int docFreq;
        int position;
        boolean useAdvance;
        int posFreq = 0;
        int pos = -1;
        int posTime = 0;
        
        public PostingAndFreq(DocsAndPositionsEnum posEnum, int docFreq, int position, boolean useAdvance) {
            this.posEnum = posEnum;
            this.docFreq = docFreq;
            this.position = position;
            this.useAdvance = useAdvance;
        }
     
        @Override
        public int compareTo(PostingAndFreq other) {
            if (docFreq != other.docFreq) {
                return docFreq - other.docFreq;
            }
            if (position != other.position) {
                return position - other.position;
            }
            return 0;
        }
    }
    
    protected class ExactPhraseDocIdSet extends DocIdSet {
        protected final AtomicReaderContext context;
        protected final Bits acceptDocs;
        protected final PostingAndFreq[] postings;
        protected boolean noDocs = false;
        
        public ExactPhraseDocIdSet(AtomicReaderContext context, Bits acceptDocs) throws IOException {
            this.context = context;
            this.acceptDocs = acceptDocs;
            
            Terms fieldTerms = context.reader().fields().terms(fieldName);
            // TermContext states[] = new TermContext[terms.size()];
            postings = new PostingAndFreq[terms.size()];
            
            TermsEnum te = fieldTerms.iterator(null);
            for (int i = 0; i < terms.size(); ++i) {
                final Term t = terms.get(i);
                // states[i] = TermContext.build(context, terms.get(i), true);
                // final TermState state = states[i].get(context.ord);
                if (!te.seekExact(t.bytes(), true)) {
                    noDocs = true;
                    return;
                }
                if (i == 0) {
                    postings[i] = new PostingAndFreq(te.docsAndPositions(acceptDocs, null, 0), te.docFreq(), positions.get(i), false);
                } else {
                    postings[i] = new PostingAndFreq(te.docsAndPositions(acceptDocs, null, 0), te.docFreq(), positions.get(i), te.docFreq() > 5 * postings[0].docFreq);
                }
            }
            
            ArrayUtil.mergeSort(postings);
            for (int i = 1; i < terms.size(); ++i) {
                postings[i].posEnum.nextDoc();
            }
        }
        
        @Override
        public DocIdSetIterator iterator() throws IOException
        {
            if (noDocs) {
                return EMPTY_DOCIDSET.iterator();
            } else {
                return new ExactPhraseDocIdSetIterator(context, acceptDocs);
            }
        }
        
        protected class ExactPhraseDocIdSetIterator extends DocIdSetIterator {
            protected int docID = -1;
            
            public ExactPhraseDocIdSetIterator(AtomicReaderContext context, Bits acceptDocs) throws IOException {
            }
            
            @Override
            public int nextDoc() throws IOException {
                while (true) {
                    // first (rarest) term
                    final int doc = postings[0].posEnum.nextDoc();
                    if (doc == DocIdSetIterator.NO_MORE_DOCS) {
                        // System.err.println("END");
                        return docID = doc;
                    }
                    
                    // non-first terms
                    int i = 1;
                    while (i < postings.length) {
                        final PostingAndFreq pf = postings[i];
                        int doc2 = pf.posEnum.docID();
                        if (pf.useAdvance) {
                            if (doc2 < doc) {
                                doc2 = pf.posEnum.advance(doc);
                            }
                        } else {
                            int iter = 0;
                            while (doc2 < doc) {
                                if (++iter == 50) {
                                    doc2 = pf.posEnum.advance(doc);
                                } else {
                                    doc2 = pf.posEnum.nextDoc();
                                }
                            }
                        }
                        if (doc2 > doc) {
                            break;
                        }
                        ++i;
                    }
                    
                    if (i == postings.length) {
                        // System.err.println(doc);
                        docID = doc;
                        // return docID;
                        if (containsPhrase()) {
                            return docID;
                        }
                    }
                }
            }
            
            @Override
            public int advance(int target) throws IOException {
                throw new IOException();
            }
            
            private boolean containsPhrase() throws IOException {
                int index = -1;
                int i = 0;
                PostingAndFreq pf;
                
                // init.
                for (i = 0; i < postings.length; ++i) {
                    postings[i].posFreq = postings[i].posEnum.freq();
                    postings[i].pos = postings[i].posEnum.nextPosition() - postings[i].position;
                    postings[i].posTime = 1;
                }
                
                while (true) {
                    pf = postings[0];
                    
                    // first term.
                    while (pf.pos < index && pf.posTime < pf.posFreq) {
                        pf.pos = pf.posEnum.nextPosition() - pf.position;
                        ++pf.posTime;
                    }
                    if (pf.pos >= index) {
                        index = pf.pos;
                    } else if (pf.posTime == pf.posFreq) {
                        return false;
                    }
                    
                    // other terms.
                    for (i = 1; i < postings.length; ++i) {
                        pf = postings[i];
                        while (pf.pos < index && pf.posTime < pf.posFreq) {
                            pf.pos = pf.posEnum.nextPosition() - pf.position;
                            ++pf.posTime;
                        }
                        if (pf.pos > index) {
                            index = pf.pos;
                            break;
                        }
                        if (pf.pos == index) {
                            continue;
                        }
                        if (pf.posTime == pf.posFreq) {

                            return false;
                        }
                    }
                    if (i == postings.length) {
                        return true;
                    }
                }
            }

            @Override
            public int docID()
            {
                return docID;
            }
        }

    }
    
}

UT:

import java.io.IOException;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.standard.StandardAnalyzer;

import org.apache.lucene.codecs.Codec;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.TextField;
import org.apache.lucene.document.Field.Store;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.IndexWriterConfig.OpenMode;
import org.apache.lucene.search.ConstantScoreQuery;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.TopDocs;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RAMDirectory;
import org.apache.lucene.util.Version;
import org.testng.annotations.AfterTest;
import org.testng.annotations.BeforeTest;
import org.testng.annotations.Test;

import com.dp.arts.lucenex.codec.Dp10Codec;

public class ExactPhraseFilterTest
{
    final Directory dir = new RAMDirectory();
    
    @BeforeTest
    public void setUp() throws IOException {
        Analyzer analyzer = new StandardAnalyzer(Version.LUCENE_40);
        IndexWriterConfig iwc = new IndexWriterConfig(Version.LUCENE_40, analyzer);
        iwc.setOpenMode(OpenMode.CREATE);
        iwc.setCodec(Codec.forName(Dp10Codec.DP10_CODEC_NAME));
        
        IndexWriter writer = new IndexWriter(dir, iwc); 
        addDocument(writer, "新疆烧烤");  // 0
        addDocument(writer, "啤酒");  // 1
        addDocument(writer, "烤烧");  // 2
        addDocument(writer, "烧烧烧");  // 3
        addDocument(writer, "烤烧中华烧烤"); // 4
        writer.close();
    }
    
    private void addDocument(IndexWriter writer, String str) throws IOException {
        Document doc = new Document();
        doc.add(new TextField("searchkeywords", str, Store.YES));
        writer.addDocument(doc, new StandardAnalyzer(Version.LUCENE_40));
    }
    
    @AfterTest
    public void tearDown() throws IOException
    {
        this.dir.close();
    }
    
    @Test
    public void test1() throws IOException
    {
        IndexReader reader = DirectoryReader.open(dir);
        IndexSearcher searcher = new IndexSearcher(reader);
        
        ExactPhraseFilter pf = new ExactPhraseFilter();
        pf.add(new Term("searchkeywords", "烧"));
        pf.add(new Term("searchkeywords", "烤"));
        Query query = new ConstantScoreQuery(pf);
        TopDocs results = searcher.search(query, 20);
        
        assert results.totalHits == 2;
        assert results.scoreDocs[0].doc == 0;
        assert results.scoreDocs[1].doc == 4;
        
        searcher.getIndexReader().close();
    }
}