GET /book-index/_search
{
   "knn": {
      "field": "title_vector",
      "query_vector": [0.1, 0.2, 0.3 ...],
      "k": 10,  // 返回的 top k 结果数量
      "num_candidates": 100  // 指定每个分片上要检索的候选向量数量
  }
  "fields": ["id", "title_text", "category"],
  "_source": false,
}


GET /book-index/_search
{
  "query": {
    "bool": {
      "should": [
        {
          "knn": {
            "field": "title_vector",
            "query_vector": [0.1, 0.2, 0.3 ...], 
            "k": 5,
            "num_candidates": 50,
            "boost": 0.8
          }
        },
        {
          "knn": {
            "field": "content_vector", 
            "query_vector": [0.1, 0.2, 0.3, ...], 
            "k": 5,
            "num_candidates": 50,
            "boost": 0.2
          }
        }
      ]
    }
  }
}