Java elasticsearch scroll模板实现

一、scroll说明和使用场景

scroll的使用场景：大数据量的检索和操作

scroll顾名思义，就是游标的意思，核心的应用场景就是遍历 elasticsearch中的数据；

通常我们遍历数据采用的是分页，elastcisearch还支持from size的方式进行分页查询，使用 from and size 的深度分页，比如说 ?size=10&from=10000，因为 100,000 排序的结果必须从每个分片上取出并重新排序最后返回 10 条。这个过程需要对每个请求页重新进行提取+排序，效率很低，消耗很大，所以默认的最大可分页的数据是10000，超过10000是不建议的；

使用

通过在url末尾带上scroll=1m表示开启一个游标，1m表示游标的有效期为1分钟

POST /record/_search?scroll=1m
{
  "from": 0,
  "size": 20
}

返回结果中会把scroll的id带上，再次查询的时候，直接用scroll id查询即可

POST /_search/scroll
{
    "scroll" : "1m", 
    "scroll_id" : "FGluY2x1ZGVfY29udGV4dF91dWlkDnF1ZXJ5VGhlbkZldGNoAhZuYmpMbVpwWFRUMnNFMUFFSHlSMHB3AAAAAALBy_0WUWxrNTRTaWNUcy1sOHQ0VUo5dzF6dxZoemFkZTlMeFQ4MmoyOW5SUG8ybE53AAAAAAN6ip8WMmk5TWZlQ21RQnFsNURwaXRzSGhCdw==" 
}

二、基于ElasticsearchRestTemplate的实现

这里我们定义了一个template如下，主要作用就是实现一个基于scroll的数据遍历模板，屏蔽开启scroll 以及 scroll遍历所有数据，通过Consumer<T>钩子函数进行数据处理

import lombok.extern.slf4j.Slf4j;
import org.elasticsearch.index.query.BoolQueryBuilder;
import org.elasticsearch.index.query.QueryBuilders;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.elasticsearch.core.ElasticsearchRestTemplate;
import org.springframework.data.elasticsearch.core.SearchHit;
import org.springframework.data.elasticsearch.core.SearchScrollHits;
import org.springframework.data.elasticsearch.core.mapping.IndexCoordinates;
import org.springframework.data.elasticsearch.core.query.NativeSearchQueryBuilder;

import java.util.List;
import java.util.concurrent.*;

/**
 * scrollTemplate 模板，用于遍历整个Index的数据
 * @author xiuzhu
 * @Date 2023/7/28 13:12
 */
@Slf4j
public class ElasticSearchScrollTemplate<T> {

    ExecutorService executorService = new ThreadPoolExecutor(1, 4,
                                      30,TimeUnit.SECONDS,
                                      new LinkedBlockingQueue<Runnable>(5),
                                        Executors.defaultThreadFactory(),
                                        new ThreadPoolExecutor.CallerRunsPolicy()
                                    );

    ElasticsearchRestTemplate elasticSearchRestTemplate;

    Class<T> cls;

    String indexName;

    public ElasticSearchScrollTemplate(
            ElasticsearchRestTemplate template,
            Class<T> cls,
            String indexName
    ) {
        this.elasticSearchRestTemplate = template;
        this.cls = cls;
        this.indexName = indexName;
    }

    @FunctionalInterface
    public interface Consumer<T> {
        public void accept(List<T> objects);
    }

    public void execute(Consumer<T> consumer) {
        //构建查询条件
        NativeSearchQueryBuilder query = new NativeSearchQueryBuilder();
        BoolQueryBuilder queryBuilder = QueryBuilders.boolQuery();

        query.withPageable(PageRequest.of(0, 300));
        query.withQuery(queryBuilder);

        //保留0.5分钟
        long scrollTimeInMillis = 30*1000;

        IndexCoordinates recordIndex = IndexCoordinates.of(indexName);
        SearchScrollHits<T> hits = elasticSearchRestTemplate.searchScrollStart(scrollTimeInMillis, query.build(), cls, recordIndex);

        // scrollId
        String scrollId = hits.getScrollId();
        List<T> recordEntityList = hits.stream().map(SearchHit::getContent).toList();
        long total = 0L;

        log.info("================ began scroll index={} ====================", indexName);

        executorService.submit(()->{
            consumer.accept(recordEntityList);
        });

        total = total + recordEntityList.size();

        log.info("================  has scroll index={} total={} ====================", indexName, total);
        while (!hits.isEmpty()) {
            hits = elasticSearchRestTemplate.searchScrollContinue(scrollId, scrollTimeInMillis, cls, recordIndex);
            List<T> entities = hits.stream().map(SearchHit::getContent).toList();

            executorService.submit(()->{
                consumer.accept(entities);
            });

            total = total + entities.size();
            try {
                //给系统留GC时间，不然容易内存溢出
                Thread.sleep(300);
            } catch (InterruptedException e) {
                log.error("sleep error", e);
            }
            log.info("================  has scroll index={} total={} ====================", indexName, total);
        }
        log.info("================ end scroll index={} ====================", indexName);
    }
}

使用参考：

@Resource(name = "elasticSearchRestTemplate")
    ElasticsearchRestTemplate elasticsearchRestTemplate;

new ElasticSearchScrollTemplate<>(
                        elasticsearchRestTemplate,
                        RecordEntity.class,
                        "record")
                ).execute((entities)->{
                    entities.forEach(item->{
                        //这里进行数据的处理，比如修改数据
                        recordEntityService.save(item);
                        log.info("tag update success record={} api={}", item.getId());

                    });
                });

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