elasticsearch 집합 함수로distinct 조회 실현

자세히 보기
1. 등가의 sql

SELECT DISTINCT field1,field2 FROM test_index.test_type

등가

SELECT field1,field2 FROM test_index.test_type GROUP BY field1,field2

 
2. Group by 쿼리는 es에서 Aggregation (집합) 으로 구현할 수 있습니다. 등가의 DSL 쿼리 문장은 다음과 같습니다.

POST /test_index/test_type/_search
{
	"from": 0,
	"size": 0,
	"aggregations": {
		"field1": {
			"terms": {
				"field": "field1",
				"size": 2147483647
			},
			"aggregations": {
				"field2": {
					"terms": {
						"field": "field2",
						"size": 2147483647
					}
				}
			}
		}
	}
}

 
3.java의 실현:

import com.google.common.collect.ArrayListMultimap;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Stack;
import java.util.stream.Collectors;
import org.elasticsearch.action.search.SearchRequestBuilder;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.Client;
import org.elasticsearch.search.aggregations.AggregationBuilders;
import org.elasticsearch.search.aggregations.bucket.terms.Terms;
import org.elasticsearch.search.aggregations.bucket.terms.TermsBuilder;

/**
 *
 * @author zhongchenghui
 */
public class EsSearch {

    private static final String CLUSTER_NAME = "test_cluster";
    private static final String ES_ADDRESSES = "192.168.12.1,192.168.12.2,192.168.12.3";
    private static final String INDEX_NAME = "test_index";
    private static final Client ES_CLIENT = ESClientFactory.newInstance(CLUSTER_NAME, ES_ADDRESSES);

    /**
     *  group by 
     *
     * @param type
     * @param groupColumnsNames
     * @return
     * @throws Exception
     */
    public List

 

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.elasticsearch.client.Client;
import org.elasticsearch.client.transport.TransportClient;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.transport.InetSocketTransportAddress;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 *
 * @author zhongchenghui
 */
public class ESClientFactory {

    private static final Logger LOGGER = LoggerFactory.getLogger(ESClientFactory.class);
    private static final ConcurrentHashMap CLIENT_CACHE = new ConcurrentHashMap<>();

    public static Client newInstance(String clusterName, String hostStr) {
        Client client = CLIENT_CACHE.get(clusterName);
        if (client == null) {
            Map addressMap = ESClientFactory.getESAddressMap(hostStr);
            Settings settings = Settings.settingsBuilder().put("cluster.name", clusterName).build();
            TransportClient newClient = TransportClient.builder().settings(settings).build();
            addressMap.keySet().forEach((host) -> {
                try {
                    newClient.addTransportAddress(new InetSocketTransportAddress(InetAddress.getByName(host), addressMap.get(host)));
                } catch (UnknownHostException ex) {
                    LOGGER.error("Init ES client failure,cluster name is:{},Error:{}", clusterName, ex);
                }
            });
            client = newClient;
            CLIENT_CACHE.put(clusterName, newClient);
        }
        return client;
    }

    private static Map getESAddressMap(String hostStr) {
        Map hostMap = new HashMap<>();
        String[] hosts = hostStr.split(",");
        for (String host : hosts) {
            String[] hostPort = host.trim().split(":");
            Integer port = hostPort.length < 2 ? 9300 : Integer.valueOf(hostPort[1]);
            hostMap.put(hostPort[0], port);
        }
        return hostMap;
    }
}

 4.문제점:
a. 구현된 방식은 층층이 아래로 집합되기 때문에es의document에field1의 필드가null일 때 이 조건은 아래로 집합되지 않습니다. 설령 이document의field2 필드가 값이 있더라도.(null 대신 지정한 문자를 사용해서 이 문제를 해결할 수 있습니다)
b. 데이터 양이 너무 많은 테이블에 적합하지 않습니다. 3의 코드는 최대 각 필드의 그룹 수가 Integer보다 크면 안 됩니다.MAX_VALUE
c. 되돌아오는 필드는 그룹by에 참여하는 필드만 가능합니다.