Lucene中关于FSDirectory和RAMDirectory的疑问
为了验证RAMDirectory的性能总是比FSDirectory好，做了一个实验。创建两个索引，一个基于FSDirectory，另一个基于RAMDirectory，每个索引都包含了3000个具有相同内容的文档。结果发现如果先建立FSDirectory的索引，则FSDirectory的速度比较快。先建立RAMDirectory的话，RAMDirectory快。
这些测试结果
1.先建立RAMDirectory
RAMDirectory Time: 94 ms
FSDirectory Time : 531 ms
2.先建立FSDirectory
RAMDirectory Time: 359 ms
FSDirectory Time : 328 ms
哪为牛人能告知我一下原因啊。。十分感谢
这是测试代码，lucene in action中的源码
package lucenedemo.test;import java.io.File;import org.apache.lucene.store.Directory;import org.apache.lucene.store.FSDirectory;import org.apache.lucene.store.RAMDirectory;import org.apache.lucene.document.Document;import org.apache.lucene.document.Field;import org.apache.lucene.index.IndexWriter;import org.apache.lucene.analysis.SimpleAnalyzer;import junit.framework.TestCase;import java.io.IOException;import java.util.Collection;import java.util.ArrayList;import java.util.Iterator;/** * */public class FSversusRAMDirectoryTest extends TestCase { private Directory fsDir; private Directory ramDir; private Collection docs = loadDocuments(3000, 5); @Override protected void setUp() throws Exception { ramDir = new RAMDirectory(); fsDir = FSDirectory.open(new File("d:\\index")); } public void testTiming() throws IOException { //如果这两个操作调换位置，结果是不同的 long ramTiming = timeIndexWriter(ramDir); long fsTiming = timeIndexWriter(fsDir); System.out.println("RAMDirectory Time: " + (ramTiming) + " ms"); System.out.println("FSDirectory Time : " + (fsTiming) + " ms"); assertTrue(fsTiming > ramTiming); } private long timeIndexWriter(Directory dir) throws IOException { long start = System.currentTimeMillis(); addDocuments(dir); long stop = System.currentTimeMillis(); return (stop - start); } private void addDocuments(Directory dir) throws IOException { IndexWriter writer = new IndexWriter(dir, new SimpleAnalyzer(),true,IndexWriter.MaxFieldLength.UNLIMITED); // change to adjust performance of indexing with FSDirectory writer.setMergeFactor(100); for (Iterator iter = docs.iterator(); iter.hasNext();) { Document doc = new Document(); String word = (String) iter.next(); doc.add(new Field("keyword", word,Field.Store.YES,Field.Index.NOT_ANALYZED)); doc.add(new Field("unindexed", word,Field.Store.YES,Field.Index.NO)); doc.add(new Field("unstored", word,Field.Store.NO,Field.Index.ANALYZED)); doc.add(new Field("text", word,Field.Store.YES,Field.Index.ANALYZED)); writer.addDocument(doc); } writer.optimize(); writer.close(); } private Collection loadDocuments(int numDocs, int wordsPerDoc) { Collection docCollection = new ArrayList(numDocs); for (int i = 0; i < numDocs; i++) { StringBuilder doc = new StringBuilder(wordsPerDoc); for (int j = 0; j < wordsPerDoc; j++) { doc.append("Bibamus "); } docCollection.add(doc.toString()); } return docCollection; }}private Collection docs = loadDocuments(300000, 5);