计算Lucene术语文件数量的最快方法

时间：2014-10-17 10:28:06

标签： java lucene

我想在Lucene中计算一个字段上的术语数量。 我知道有3种方法可以做到这一点;我很好奇最好和最快的做法是什么：

我将在一个长类型的单值字段（“字段”）中搜索该术语（所以不是文本，而是编号数据！）

以下任何一个预编码代码将首先使用：

Directory dirIndex = FSDirectory.open('/path/to/index/');
IndexReader indexReader = DirectoryReader.open(dirIndex);
final BytesRefBuilder bytes = new BytesRefBuilder(); 
NumericUtils.longToPrefixCoded(Long.valueOf(longTerm).longValue(),0,bytes);

1）使用Index

中的docFreq（） 
TermsEnum termEnum = MultiFields.getTerms(indexReader, "field").iterator(null);
termEnum.seekExact(bytes.toBytesRef());
int count = termEnum.docFreq();

2）搜索

IndexSearcher searcher = new IndexSearcher(indexReader);
TermQuery query = new TermQuery(new Term("field", bytes.toBytesRef()));
TotalHitCountCollector collector = new TotalHitCountCollector();
searcher.search(query,collector);
int count = collector.getTotalHits();

3）从索引中读取完全匹配并逐个计算文档

TermsEnum termEnum = MultiFields.getTerms(indexReader, "field").iterator(null);
termEnum.seekExact(bytes.toBytesRef());
Bits liveDocs = MultiFields.getLiveDocs(indexReader);
DocsEnum docsEnum = termEnum.docs(liveDocs, null);
int count = 0;
if (docsEnum != null) {
    int docx;
    while ((docx = docsEnum.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
        count++;
    }
 }

最佳方法

选项1）获得最短代码，但如果您更新和删除索引中的文档，则基本无用。它会将已删除的文档统计为好像它们仍在那里。许多地方没有记录（官方文档除外，但在s.o.的答案中没有记录），这是需要注意的。也许有一种解决方法，否则对这种方法的热情有点错位。 选项2）和3）确实产生了正确的结果，但哪个应该是首选？或者更好 - 有更快的方法吗？

1 个答案:

答案 0 :(得分：2)

通过测试来衡量，使用索引来获取文档而不是搜索它们（即选项3而不是选项2）似乎更快（平均值：选项3）在100中快8倍doc sample 我可以运行）。 我也改变了测试，以确保在另一个之前运行一个不会影响结果：它没有。

所以看起来搜索者正在创建一些执行简单文档计数的开销，如果考虑计算单个术语条目的文档，则索引中的查找速度最快。

用于测试的代码（使用SOLR索引中的前100条记录）：

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.Fields;
import org.apache.lucene.index.DocsEnum;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.MultiFields;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;
import org.apache.lucene.util.NumericUtils;
import org.apache.lucene.queryparser.classic.ParseException;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.TermQuery;
import org.apache.lucene.search.TotalHitCountCollector;
import org.apache.lucene.util.Bits;
import org.apache.lucene.index.MultiFields;

public class ReadLongTermReferenceCount {

    public static void main(String[] args) throws IOException {

        Directory dirIndex = FSDirectory.open('/path/to/index/');
        IndexReader indexReader = DirectoryReader.open(dirIndex);
        final BytesRefBuilder bytes = new BytesRefBuilder(); 


        TermsEnum termEnum = MultiFields.getTerms(indexReader, "field").iterator(null);

        IndexSearcher searcher = new IndexSearcher(indexReader);
        TotalHitCountCollector collector = new TotalHitCountCollector();

        Bits liveDocs = MultiFields.getLiveDocs(indexReader);
        final BytesRefBuilder bytes = new BytesRefBuilder(); // for reuse!
        int maxDoc = indexReader.maxDoc();
        int docsPassed = 0;
        for (int i=0; i<maxDoc; i++) {
            if (docsPassed==100) {
                break;
            }
            if (liveDocs != null && !liveDocs.get(i))
                continue;
            Document doc = indexReader.document(i);

            //get longTerm from this doc and convert to BytesRefBuilder
            String longTerm = doc.get("longTerm");
            NumericUtils.longToPrefixCoded(Long.valueOf(longTerm).longValue(),0,bytes);

            //time before the first test
            long time_start = System.nanoTime();

            //look in the "field" index for longTerm and count the number of documents
            int count = 0;
            termEnum.seekExact(bytes.toBytesRef());
            DocsEnum docsEnum = termEnum.docs(liveDocs, null);
            if (docsEnum != null) {
                int docx;
                while ((docx = docsEnum.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
                    count++;
                }
            }

            //mid point: test 1 done, start of test 2
            long time_mid = System.nanoTime();

            //do a search for longTerm in "field"
            TermQuery query = new TermQuery(new Term("field", bytes.toBytesRef()));
            searcher.search(query,collector);
            int count = collector.getTotalHits();

            //end point: test 2 done.
            long time_end = System.nanoTime();

            //write to stdout
            System.out.println(longTerm+"\t"+(time_mid-time_start)+"\t"+(time_end-time_mid));

            docsPassed++;
        }
        indexReader.close();
        dirIndex.close();
    }
}

稍微修改上面的内容以使用Lucene 5：

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.Fields;
import org.apache.lucene.index.PostingsEnum;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.MultiFields;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;
import org.apache.lucene.util.NumericUtils;
import org.apache.lucene.queryparser.classic.ParseException;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.TermQuery;
import org.apache.lucene.search.TotalHitCountCollector;
import org.apache.lucene.util.Bits;
import org.apache.lucene.index.MultiFields;

public class ReadLongTermReferenceCount {

    public static void main(String[] args) throws IOException {

        Directory dirIndex = FSDirectory.open(Paths.get('/path/to/index/'));
        IndexReader indexReader = DirectoryReader.open(dirIndex);
        final BytesRefBuilder bytes = new BytesRefBuilder(); 


        TermsEnum termEnum = MultiFields.getTerms(indexReader, "field").iterator(null);

        IndexSearcher searcher = new IndexSearcher(indexReader);
        TotalHitCountCollector collector = new TotalHitCountCollector();

        Bits liveDocs = MultiFields.getLiveDocs(indexReader);
        final BytesRefBuilder bytes = new BytesRefBuilder(); // for reuse!
        int maxDoc = indexReader.maxDoc();
        int docsPassed = 0;
        for (int i=0; i<maxDoc; i++) {
            if (docsPassed==100) {
                break;
            }
            if (liveDocs != null && !liveDocs.get(i))
                continue;
            Document doc = indexReader.document(i);

            //get longTerm from this doc and convert to BytesRefBuilder
            String longTerm = doc.get("longTerm");
            NumericUtils.longToPrefixCoded(Long.valueOf(longTerm).longValue(),0,bytes);

            //time before the first test
            long time_start = System.nanoTime();

            //look in the "field" index for longTerm and count the number of documents
            int count = 0;
            termEnum.seekExact(bytes.toBytesRef());
            PostingsEnum docsEnum = termEnum.postings(liveDocs, null);
            if (docsEnum != null) {
                int docx;
                while ((docx = docsEnum.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
                    count++;
                }
            }

            //mid point: test 1 done, start of test 2
            long time_mid = System.nanoTime();

            //do a search for longTerm in "field"
            TermQuery query = new TermQuery(new Term("field", bytes.toBytesRef()));
            searcher.search(query,collector);
            int count = collector.getTotalHits();

            //end point: test 2 done.
            long time_end = System.nanoTime();

            //write to stdout
            System.out.println(longTerm+"\t"+(time_mid-time_start)+"\t"+(time_end-time_mid));

            docsPassed++;
        }
        indexReader.close();
        dirIndex.close();
    }
}
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