Elasticsearch:执行同样的查询语句多次结果不一致？！

GET test/_search
{
  "query": {
    "match": {
      "title": "中国"
    }
  },
  "min_score": 2.0
}

POST cc/c/1
{
	"x":"ab abc abc"
}

PUT cc/c/1
{
	"x":"abc abc abc abc"
}

	DELETE cc/c/5

POST cc/_forcemerge?only_expunge_deletes=true

GET _cat/segments/cc

GET cc/c/_search?preference=_primary

	{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 3,
    "max_score": 4.205637,
    "hits": [
      {
        "_index": "cc",
        "_type": "c",
        "_id": "1",
        "_score": 4.205637,
        "_source": {
          "x": "abc"
        }
      },
      {
        "_index": "cc",
        "_type": "c",
        "_id": "5",
        "_score": 1.7646677,
        "_source": {
          "x": "abc a c"
        }
      },
      {
        "_index": "cc",
        "_type": "c",
        "_id": "8",
        "_score": 1.7646677,
        "_source": {
          "x": "abc ax c"
        }
      }
    ]
  }
}

	{
  "took": 0,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 3,
    "max_score": 4.205637,
    "hits": [
      {
        "_index": "cc",
        "_type": "c",
        "_id": "1",
        "_score": 4.205637,
        "_source": {
          "x": "abc"
        }
      },
      {
        "_index": "cc",
        "_type": "c",
        "_id": "5",
        "_score": 1.8076806,
        "_source": {
          "x": "abc a c"
        }
      },
      {
        "_index": "cc",
        "_type": "c",
        "_id": "8",
        "_score": 1.8076806,
        "_source": {
          "x": "abc ax c"
        }
      }
    ]
  }
}

	public Explanation idfExplain(CollectionStatistics collectionStats, TermStatistics termStats) {
    final long df = termStats.docFreq();
    final long docCount = collectionStats.docCount() == -1 ? collectionStats.maxDoc() : collectionStats.docCount();
    final float idf = idf(df, docCount);
    return Explanation.match(idf, "idf, computed as log(1 + (docCount - docFreq + 0.5) / (docFreq + 0.5)) from:",
        Explanation.match(df, "docFreq"),
        Explanation.match(docCount, "docCount"));
  }

	/** returns the total number of documents, regardless of 
	   * whether they all contain values for this field. 
	   * @see IndexReader#maxDoc() */
	  public final long maxDoc() {
	    return maxDoc;
	  }
	  
	  /** returns the total number of documents that
	   * have at least one term for this field. 
	   * @see Terms#getDocCount() */
	  public final long docCount() {
	    return docCount;
	  }

/** Returns one greater than the largest possible document number.
   * This may be used to, e.g., determine how big to allocate an array which
   * will have an element for every document number in an index.
   */
  public abstract int maxDoc();

/** Returns the number of documents that have at least one
   *  term for this field, or -1 if this measure isn't
   *  stored by the codec.  Note that, just like other term
   *  measures, this measure does not take deleted documents
   *  into account. */
  public abstract int getDocCount() throws IOException;