ElasticSearch如何一次查询出全部数据——基于Scroll

Posted 2020-11-24 naughtycat

Elasticsearch 查询结果默认只显示10条，可以通过设置from及size来达到分页的效果(详见附3），但是 from + size <= 10,000，因为index.max_result_window 默认值是10，000，而 from+ size 必须小于index.max_result_window 。因此只能用Scroll取出所有的结果，

• Scroll相当于传统数据库的游标，具体代码片段如下：

		SearchResponse scrollResp = client.prepareSearch(availableIndices)
				.setTypes(type)
				.setScroll(new TimeValue(60000))
				.setQuery(boolQueryBuilder)
				.setSize(SEARCH_HITS_SIZE).get(); //max of SEARCH_HITS_SIZE hits will be returned for each scroll
		//Scroll until no hits are returned
		do {

			for (SearchHit hit : scrollResp.getHits().getHits()) {
					tmpJsonList.add( (JSONObject) JSONValue.parse(hit.getSourceAsString()));
				}
			}
			jsonList.addAll(tmpJsonList);
			tmpJsonList.clear();
			scrollResp = client.prepareSearchScroll(scrollResp.getScrollId()).setScroll(new TimeValue(60000)).execute().actionGet();
		} while (scrollResp.getHits().getHits().length != 0);

setScroll()里传入的时间，表示一次处理setSize()里的数据超时时间。即处理一个分页最长不超过的时间，上面的代码表示1分钟。scrollResp.getScrollId()每次回生成一个ScrollID，如下图：

 

• 用from + size循环读取的代码片段如下：

　　　　　　 int index = 0; 
            {
                tmpJsonList.clear();
                srb.setFrom(Math.multiplyExact(index, SEARCH_HITS_SIZE));
                index++;
                MultiSearchResponse.Item[] items = sr.get().getResponses();
                for (MultiSearchResponse.Item item : items) {
                    SearchResponse response = item.getResponse();
                    SearchHit[] hits = response.getHits().getHits();
                    if (hits.length != 0) {
                        for (SearchHit hit : hits) {
                                tmpJsonList.add((JSONObject) JSONValue.parse(hit.getSourceAsString());
                            }
                        }
                    }
                jsonList.addAll(tmpJsonList);
                }
            } while (tmpJsonList.size() > 0);

其中：SEARCH_HITS_SIZE = 1000， srb是多条件组合查询，前置代码如下：

 queryBuilders.forEach(query -> {          
        boolQueryBuilder.must(query);
            });

MultiSearchRequestBuilder sr = client.prepareMultiSearch();
            SearchRequestBuilder srb = client.prepareSearch().setTypes(type).setIndices(availableIndices).setQuery(boolQueryBuilder).setSize(SEARCH_HITS_SIZE);
            sr.add(srb);

查询条件的构造代码片段如下（用QueryBuilders根据需要选择term, range, match等）：

	StringUtil.isEmpty(l7p)) {
            queryBuilders.add(QueryBuilders.termQuery(Event.FIELD_L7P, l7p));
        }
  
        if (!StringUtil.isEmpty(startTime) && StringUtil.isEmpty(endTime)) {
            queryBuilders.add(QueryBuilders.rangeQuery(Event.FIELD_START_TIME).from(startTime));
        }

 

附：

1）using scroll in java https://www.elastic.co/guide/en/elasticsearch/client/java-api/current/java-search-scrolling.html

2）scroll https://www.elastic.co/guide/en/elasticsearch/reference/5.1/search-request-scroll.html

3) from and size https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-body.html#request-body-search-from-size

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