ElasticSearch Scroll API 大量数据查询

ElasticSearch 要查询大量数据的时候，比如全量数据遍历的时候，最好使用scroll search api。

1. 初始化Scroll Context

SearchRequest searchRequest = new SearchRequest("posts");
SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
searchSourceBuilder.query(matchQuery("title", "Elasticsearch"));
searchSourceBuilder.size(size); 
searchRequest.source(searchSourceBuilder);
searchRequest.scroll(TimeValue.timeValueMinutes(1L)); 
SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);
String scrollId = searchResponse.getScrollId(); 
SearchHits hits = searchResponse.getHits();  

这里需要设置size的大小（每一页多少数据），同时也需要设置scroll 告诉每个scroll保留多长时间，这里的时间是处理完每页所用的时间。

2. 检索相关数据

SearchScrollRequest scrollRequest = new SearchScrollRequest(scrollId); 
scrollRequest.scroll(TimeValue.timeValueS