lucene NRT实时目录学习

lucene NRT实时索引学习

? ? ?lucene高级版本中添加了对实时索引查询的功能，因为在真实的应用场景中经常会对IndexWriter做写，更新或者删除操作之后马上去做查询操作，之前较低的版本中必要执行commit操作后将索引都写到磁盘之后才能从IndexSearcher 对象上的查询才能更新，老方式比较耗时。

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? ? ? 实例代码如下：

public class LuceneNrtTest extends TestCase {public static Analyzer analyzer;static {analyzer = new StandardAnalyzer(Version.LUCENE_31);}public void testNearRealTime() throws Exception {Directory dir = new RAMDirectory();IndexWriterConfig iwc = new IndexWriterConfig(Version.LUCENE_31,analyzer);iwc.setOpenMode(OpenMode.CREATE_OR_APPEND);IndexWriter writer = new IndexWriter(dir, iwc);for (int i = 0; i < 10; i++) {Document doc = new Document();doc.add(new Field("id", "" + i, Field.Store.NO,Field.Index.NOT_ANALYZED_NO_NORMS));doc.add(new Field("text", "aaa", Field.Store.NO,Field.Index.ANALYZED));writer.addDocument(doc);}// 测试是否能查询到刚刚插入的数据IndexReader reader = IndexReader.open(writer, false);IndexSearcher searcher = new IndexSearcher(reader);Query query = new TermQuery(new Term("text", "aaa"));TopDocs docs = searcher.search(query, 1);assertEquals(10, docs.totalHits);// 测试是否能删除一条数据writer.deleteDocuments(new Term("id", "7"));// 再加一条Document doc = new Document();doc.add(new Field("id", "11", Field.Store.NO,Field.Index.NOT_ANALYZED_NO_NORMS));doc.add(new Field("text", "bbb", Field.Store.NO, Field.Index.ANALYZED));writer.addDocument(doc);IndexReader newReader = IndexReader.open(writer, true);assertFalse(reader == newReader);reader.close();searcher = new IndexSearcher(newReader);TopDocs hits = searcher.search(query, 10);assertEquals(9, hits.totalHits);query = new TermQuery(new Term("text", "bbb"));hits = searcher.search(query, 1);assertEquals(1, hits.totalHits);newReader.close();writer.close();}}

?代码所依赖的lucene版本是：

<dependency><groupId>org.apache.lucene</groupId><artifactId>lucene-core</artifactId><version>3.5.0</version></dependency>

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有一点要说明的是这里所说的实时索引，并不等同于正的实时索引，只不过接近实时索引，可能更新完条数据，马上去执行search操作，结果可能不会显示出来，要稍微等待一点时间就能查询到最新结果了（也许是十几毫秒吧），这点和数据库操作有点不一样，不过总的来说也非常好用了。

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