lucene分组查询中问题总结

最近需求中需要使用lucene的分组查询，现有API使用GroupingSearch查询，代码如下：

	GroupingSearch groupingSearch = new GroupingSearch("compId");
		groupingSearch.setGroupSort(new Sort(SortField.FIELD_SCORE));
		groupingSearch.setFillSortFields(true);
		//groupingSearch.setCachingInMB(8.0, true);
		groupingSearch.setAllGroups(true);
		// groupingSearch.setAllGroupHeads(true);
		groupingSearch.setGroupDocsLimit(10);

		IndexWriterConfig config = new IndexWriterConfig(new IKAnalyzer());
		config.setOpenMode(OpenMode.CREATE_OR_APPEND);

		LogByteSizeMergePolicy mergePolicy = new LogByteSizeMergePolicy();
		Directory directory = NIOFSDirectory.open(new File("/Users/lvyanglin/searchdata/search/offlineindex").toPath()); // 新建的文件在子目录
		mergePolicy.setMergeFactor(5);
		config.setMergePolicy(mergePolicy);
		config.setSimilarity(new ClassicSimilarity());
		IndexWriter indexWriter = new IndexWriter(directory, config);
		IndexReader reader = DirectoryReader.open(indexWriter);

		
		
		IndexSearcher isearcher = new IndexSearcher(reader);
		Query query = new TermQuery(new Term("id", "20755185"));
		
	

		TopGroups<BytesRef> result = groupingSearch.search(isearcher, query, 0, 1000);

		System.out.println("搜索命中数：" + result.totalHitCount);
		System.out.println("搜索结果分组数：" + result.groups.length);

		Document document;
		for (GroupDocs<BytesRef> groupDocs : result.groups) {
			System.out.println("分组：" + groupDocs.groupValue.utf8ToString());
			System.out.println("组内记录：" + groupDocs.totalHits);

			// System.out.println("groupDocs.scoreDocs.length:" +
			// groupDocs.scoreDocs.length);
			for (ScoreDoc scoreDoc : groupDocs.scoreDocs) {
				System.out.println("compId="+isearcher.doc(scoreDoc.doc).get("compId"));
			}
		}

	}

但是不管怎么调试都会出现：

Exception in thread "main" java.lang.IllegalStateException: unexpected docvalues type NONE for field 'compId' (expected=SORTED). Re-index with correct docvalues type.
	at org.apache.lucene.index.DocValues.checkField(DocValues.java:212)
	at org.apache.lucene.index.DocValues.getSorted(DocValues.java:264)
	at org.apache.lucene.search.grouping.term.TermFirstPassGroupingCollector.doSetNextReader(TermFirstPassGroupingCollector.java:91)
	at org.apache.lucene.search.SimpleCollector.getLeafCollector(SimpleCollector.java:33)
	at org.apache.lucene.search.MultiCollector.getLeafCollector(MultiCollector.java:121)
	at org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:660)
	at org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:473)
	at org.apache.lucene.search.grouping.GroupingSearch.groupByFieldOrFunction(GroupingSearch.java:193)
	at org.apache.lucene.search.grouping.GroupingSearch.search(GroupingSearch.java:129)
	at com.shunteng.service.test.v3.GroupSearchTest2.main(GroupSearchTest2.java:79)

问题在于分组排序字段必须为SortedDocValuesField，因为是long类型字段所以我就使用SortedNumbericDocValuesField这个字段建索引，运行后还是发生以上错误。百度基本上找个不到问题原因，官网也是没什么解释，官网wiki上也没有例子。只能debug代码来找出问题，看是在那个环节出现的异常。直接抛出异常的方法是DocValues.java中checkField方法，

private static void checkField(LeafReader in, String field, DocValuesType... expected) {
    FieldInfo fi = in.getFieldInfos().fieldInfo(field);
    if (fi != null) {
      DocValuesType actual = fi.getDocValuesType();
      throw new IllegalStateException("unexpected docvalues type " + actual + 
                                        " for field '" + field + "' " +
                                        (expected.length == 1 
                                        ? "(expected=" + expected[0]
                                        : "(expected one of " + Arrays.toString(expected)) + "). " +
                                        "Re-index with correct docvalues type.");
    }
  }

看下面方法进入此方法抛出异常，制药进入上面这个方法必定抛出异常。所以要找出为什么进入这个方法：

 public static SortedDocValues getSorted(LeafReader reader, String field) throws IOException {
    SortedDocValues dv = reader.getSortedDocValues(field);
    if (dv == null) {
      checkField(reader, field, DocValuesType.SORTED);
      return emptySorted();
    } else {
      return dv;
    }
  }

上面这个方法getSorted是关键条件，深入=reader.getSortedDocValues(field);这个方法如下

 @Override
   @Override
  public final SortedDocValues getSortedDocValues(String field) throws IOException {
    ensureOpen();
    Map<String,Object> dvFields = docValuesLocal.get();
    
    Object previous = dvFields.get(field);
    if (previous != null && previous instanceof SortedDocValues) {
      return (SortedDocValues) previous;
    } else {
      FieldInfo fi = getDVField(field, DocValuesType.SORTED);
      if (fi == null) {
        return null;
      }
      SortedDocValues dv = getDocValuesReader().getSorted(fi);
      dvFields.put(field, dv);
      return dv;
    }
  } 

这个previous instanceof SortedDocValues 如果成立 或这个后面类型为SortedDocValuesField 就不会有下面return null，问题就是在于我们配置索引分组字段的时候必须要使用SortedDocValuesField 这个类型的字段。不能使用SortedNumbericDocValuesField，来建索引，这个也是lucene奇葩地方。
我写这个文章目的是总结最近起找问题的心得，在使用阿里巴巴dubbo的时候也遇到到处找不到资料的情况，我们需要一步一步的debug出来问题根源比baidu上更靠谱速度也许更快。