[急]lucene.net 全文检索的问题

1. 建立索引到下面各个目录

  A 目录 (1.39GB)
  B 目录 (70.8MB)
  C 目录 (10.2MB)
  D 目录 (325MB)
  E 目录 (7.21MB)
  F 目录 (21.3MB)

2. 搜索单个目录时耗时 2~4 秒之间

代码如下
System.IO.DirectoryInfo[] DirInfos = new DirectoryInfo[6];
Lucene.Net.Search.IndexSearcher []Searcher = new IndexSearcher[6];
String key = String.Empty;

  DirInfos[0] = new DirectoryInfo(System.Configuration.ConfigurationManager.AppSettings["A"]);
  DirInfos[1] = new DirectoryInfo(System.Configuration.ConfigurationManager.AppSettings["B"]);
  DirInfos[2] = new DirectoryInfo(System.Configuration.ConfigurationManager.AppSettings["C"]);
  DirInfos[3] = new DirectoryInfo(System.Configuration.ConfigurationManager.AppSettings["C"]);
  DirInfos[4] = new DirectoryInfo(System.Configuration.ConfigurationManager.AppSettings["E"]);
  DirInfos[5] = new DirectoryInfo(System.Configuration.ConfigurationManager.AppSettings["F"]);



  Lucene.Net.Store.Directory IndexDir = Lucene.Net.Store.FSDirectory.Open(DirInfos[0]);
  Searcher[0] = new IndexSearcher(IndexDir, true);

  IndexDir = Lucene.Net.Store.FSDirectory.Open(DirInfos[1]);
  Searcher[1] = new IndexSearcher(IndexDir, true);

  IndexDir = Lucene.Net.Store.FSDirectory.Open(DirInfos[2]);
  Searcher[2] = new IndexSearcher(IndexDir, true);

  IndexDir = Lucene.Net.Store.FSDirectory.Open(DirInfos[3]);
  Searcher[3] = new IndexSearcher(IndexDir, true);

  IndexDir = Lucene.Net.Store.FSDirectory.Open(DirInfos[4]);
  Searcher[4] = new IndexSearcher(IndexDir, true);

  IndexDir = Lucene.Net.Store.FSDirectory.Open(DirInfos[5]);
  Searcher[5] = new IndexSearcher(IndexDir, true);

  MultiSearcher ms = new MultiSearcher(Searcher);

  Analyzer WordBreaker = new StandardAnalyzer(Lucene.Net.Util.Version.LUCENE_29);

  //Sort sort = new Sort(new SortField("PublishDate", SortField.DOC, false));

  String[] keywords={"中国","中国","中国"};
  String[] fields ={"Title","Summary","Content"};
  BooleanClause.Occur[] clause ={BooleanClause.Occur.SHOULD,BooleanClause.Occur.SHOULD,BooleanClause.Occur.SHOULD};
  Query QueryResult = MultiFieldQueryParser.Parse(Lucene.Net.Util.Version.LUCENE_29, keywords, fields, clause, WordBreaker);

DateTime now = DateTime.Now;

//得到ScoreDoc数组
sc = ms.Search(QueryResult, 9999999).scoreDocs;

这段代码耗时达 18~ 25 秒之间

问一下,大家有没有什么办法能提高搜索效率? 急~~~~~~

补充：.NET技术 ,  C#