Elasticsearch scroll 之滚动查询

Elasticsearch 的 Scroll API 是一种用于处理大规模数据集的机制，特别是在需要从索引中检索大量数据时。通常情况下，Elasticsearch 的搜索请求会有一个结果集大小的限制 (from+size 的检索数量默认是 10,000 条记录)，而 Scroll API 允许你绕过这个限制，通过滚动的方式逐步获取数据

关键概念

Scroll Context(滚动上下文)
- 当你第一次发起一个滚动请求时，Elasticsearch 会创建一个滚动上下文。这个上下文保存了搜索的状态和位置，以便在后续请求中继续检索数据
- 滚动上下文是有状态的，它在服务器端保存了一段时间 (由你指定的超时时间决定)
Scroll ID(滚动 ID)
- 每次滚动请求都会返回一个scrollId，这是一个唯一标识符，用于标识和管理滚动上下文
- 你需要在后续的滚动请求中提供这个scrollId，以便 Elasticsearch 知道从哪里继续检索数据
Timeout(超时时间)
- 你可以为滚动上下文指定一个超时时间，这个时间决定了滚动上下文在服务器端保持活跃的时间
- 如果在超时时间内没有新的滚动请求，滚动上下文会被自动清除

工作原理

初始请求
- 你首先发起一个搜索请求，并指定滚动参数 (如超时时间)。这个请求会返回初始的搜索结果和一个scrollId
后续请求
- 使用返回的scrollId发起后续的滚动请求。每个请求都会返回一批新的结果和一个新的scrollId
- 你继续使用新的scrollId进行后续请求，直到没有更多结果返回
清除滚动上下文
- 当你完成数据检索后，应该显式地清除滚动上下文，以释放服务器资源。这可以通过ClearScrollRequest来实现

Java 实现

java 复制代码

package com.xxx;

import org.elasticsearch.action.search.ClearScrollRequest;
import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.action.search.SearchScrollRequest;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.common.unit.TimeValue;
import org.elasticsearch.index.query.BoolQueryBuilder;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.SearchHit;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.enthusa.avatar.core.utils.DateUtil;
import org.enthusa.avatar.utils.task.TaskModel;
import org.springframework.stereotype.Component;


@Slf4j
@Component
public class ESScrollTask extends AbstractTask {
    
    private static final String[] INCLUDE_FIELDS = {"entity_id", "job_name", "job_city", "edu_level", "locations", "company_id", "career_job_id2", "salary"};
    private static final String[] EXCLUDE_FIELDS = {};

    public static final int ES_EACH_SIZE = 500;
    public static final int ES_TOTAL_SIZE = 10000;

    @Resource
    protected RestHighLevelClient utEsClient;

    private List<PlatformJob> termSearchWithScroll(Integer recruitType) {
        final long scrollTimeout = 60000;
        List<PlatformJob> platformJobs = new ArrayList<>();
        try {
            SearchRequest searchRequest = new SearchRequest(Constants.ES_JOB_ITEM);
            SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
			// 自定义查询语句
            searchSourceBuilder.query(buildQuery(recruitType));
            searchSourceBuilder.fetchSource(INCLUDE_FIELDS, EXCLUDE_FIELDS);
            searchSourceBuilder.size(ES_EACH_SIZE);
            searchRequest.source(searchSourceBuilder);
            // 滚动查询及超时时间
            searchRequest.scroll(TimeValue.timeValueMillis(scrollTimeout));

            SearchResponse searchResponse = utEsClient.search(searchRequest, RequestOptions.DEFAULT);
            String scrollId = searchResponse.getScrollId();
            SearchHit[] searchHits = searchResponse.getHits().getHits();

            while (searchHits != null && searchHits.length > 0 && platformJobs.size() < ES_TOTAL_SIZE) {
                for (SearchHit hit : searchHits) {
                	// 自定义业务
                    PlatformJob platformJob = new PlatformJob();
                    platformJob.setJobId(IdMapping.toId((Long) hit.getSourceAsMap().get("entity_id")));
                    platformJob.setJobName((String) hit.getSourceAsMap().get("job_name"));
                    platformJob.setJobCity((String) hit.getSourceAsMap().get("job_city"));
                    platformJob.setEducation(eduLevelMap.get((Integer) hit.getSourceAsMap().get("edu_level")));
                    platformJob.setLocations((String) hit.getSourceAsMap().get("locations"));
                    platformJob.setCompanyId((Integer) hit.getSourceAsMap().get("company_id"));
                    platformJob.setCareerJobId2((Integer) hit.getSourceAsMap().get("career_job_id2"));
                    platformJob.setSalary((String) hit.getSourceAsMap().get("salary"));
                    platformJobs.add(platformJob);
                }
				
                SearchScrollRequest scrollRequest = new SearchScrollRequest(scrollId);
                scrollRequest.scroll(TimeValue.timeValueMillis(scrollTimeout));
                searchResponse = utEsClient.scroll(scrollRequest, RequestOptions.DEFAULT);
                scrollId = searchResponse.getScrollId();
                searchHits = searchResponse.getHits().getHits();
            }

			// 清除滚动上下文
            ClearScrollRequest clearScrollRequest = new ClearScrollRequest();
            clearScrollRequest.addScrollId(scrollId);
            utEsClient.clearScroll(clearScrollRequest, RequestOptions.DEFAULT);
        } catch (Exception e) {
            log.info("es search error", e);
            return Collections.emptyList();
        }
        return platformJobs;
    }

    public BoolQueryBuilder buildQuery(Integer recruitType) {
        BoolQueryBuilder queryBuilder = QueryBuilders.boolQuery();
        queryBuilder.filter(QueryBuilders.termQuery("content_type", IdType.PLATFORM_JOB.toString()));
        queryBuilder.filter(QueryBuilders.termQuery("status", 0));
        queryBuilder.filter(QueryBuilders.termQuery("recruit_type", recruitType));
        return queryBuilder;
    }
}