Elasticsearch搜尋類型(SearchType )詳解

es在查詢時，可以指定搜尋類型為QUERY_THEN_FETCH,QUERY_AND_FEATCH,DFS_QUERY_THEN_FEATCH和DFS_QUERY_AND_FEATCH,COUNT,SCAN。

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.elasticsearch.action.search;

import org.elasticsearch.common.ParseField;
import org.elasticsearch.common.ParseFieldMatcher;

public enum SearchType {
     /**
     * Same as {@link #QUERY_THEN_FETCH}, except for an initial scatter phase which goes and computes the distributed
     * term frequencies for more accurate scoring.
     */
    DFS_QUERY_THEN_FETCH((byte) 0),
    /**
     * The query is executed against all shards, but only enough information is returned (not the document content).
     * The results are then sorted and ranked, and based on it, only the relevant shards are asked for the actual
     * document content. The return number of hits is exactly as specified in size, since they are the only ones that
     * are fetched. This is very handy when the index has a lot of shards (not replicas, shard id groups).
     */
    QUERY_THEN_FETCH((byte) 1),
    /**
     * Same as {@link #QUERY_AND_FETCH}, except for an initial scatter phase which goes and computes the distributed
     * term frequencies for more accurate scoring.
     */
    DFS_QUERY_AND_FETCH((byte) 2),
    /**
     * The most naive (and possibly fastest) implementation is to simply execute the query on all relevant shards
     * and return the results. Each shard returns size results. Since each shard already returns size hits, this
     * type actually returns size times number of shards results back to the caller.
     */
    QUERY_AND_FETCH((byte) 3),
    /**
     * Performs scanning of the results which executes the search without any sorting.
     * It will automatically start scrolling the result set.
     * @deprecated will be removed in 3.0, you should do a regular scroll instead, ordered by `_doc`
     */
    @Deprecated
    SCAN((byte) 4),
    /**
     * Only counts the results, will still execute aggregations and the like.
     * @deprecated does not any improvements compared to {@link #QUERY_THEN_FETCH} with a `size` of {@code 0}
     */
    @Deprecated
    COUNT((byte) 5);

    public static final SearchType DEFAULT = QUERY_THEN_FETCH;
    private static final ParseField COUNT_VALUE = (new ParseField("count", new String[0])).withAllDeprecated("query_then_fetch");
    private static final ParseField SCAN_VALUE = (new ParseField("scan", new String[0])).withAllDeprecated("query_then_fetch sorting on `_doc`");
    private byte id;

    private SearchType(byte id) {
        this.id = id;
    }

    public byte id() {
        return this.id;
    }

    public static SearchType fromId(byte id) {
        if(id == 0) {
            return DFS_QUERY_THEN_FETCH;
        } else if(id == 1) {
            return QUERY_THEN_FETCH;
        } else if(id == 2) {
            return DFS_QUERY_AND_FETCH;
        } else if(id == 3) {
            return QUERY_AND_FETCH;
        } else if(id == 4) {
            return SCAN;
        } else if(id == 5) {
            return COUNT;
        } else {
            throw new IllegalArgumentException("No search type for [" + id + "]");
        }
    }

    public static SearchType fromString(String searchType, ParseFieldMatcher parseFieldMatcher) {
        if(searchType == null) {
            return DEFAULT;
        } else if("dfs_query_then_fetch".equals(searchType)) {
            return DFS_QUERY_THEN_FETCH;
        } else if("dfs_query_and_fetch".equals(searchType)) {
            return DFS_QUERY_AND_FETCH;
        } else if("query_then_fetch".equals(searchType)) {
            return QUERY_THEN_FETCH;
        } else if("query_and_fetch".equals(searchType)) {
            return QUERY_AND_FETCH;
        } else if(parseFieldMatcher.match(searchType, SCAN_VALUE)) {
            return SCAN;
        } else if(parseFieldMatcher.match(searchType, COUNT_VALUE)) {
            return COUNT;
        } else {
            throw new IllegalArgumentException("No search type for [" + searchType + "]");
        }
    }
}
           

 SearchRequestBuilder有很多很實用的方法：

        (1) setIndices(String... indices)：上文中描述過，參數可為一個或多個字元串，表示要進行檢索的index；

        (2) setTypes(String... types)：參數可為一個或多個字元串，表示要進行檢索的type，當參數為0個或者不調用此方法時，表示查詢所有的type；

        (3) setSearchType(SearchType searchType)：執行檢索的類别，值為org.elasticsearch.action.search.SearchType的元素，SearchType是一個枚舉類型的類，其值如下所示：

元素    含義

QUERY_THEN_FETCH    查詢是針對所有的塊執行的，但傳回的是足夠的資訊，而不是文檔内容（Document）。結果會被排序和分級，基于此，隻有相關的塊的文檔對象會被傳回。由于被取到的僅僅是這些，故而傳回的hit的大小正好等于指定的size。這對于有許多塊的index來說是很便利的（傳回結果不會有重複的，因為塊被分組了）。

QUERY_AND_FETCH    最原始（也可能是最快的）實作就是簡單的在所有相關的shard上執行檢索并傳回結果。每個shard傳回一定尺寸的結果。由于每個shard已經傳回了一定尺寸的hit，這種類型實際上是傳回多個shard的一定尺寸的結果給調用者。

DFS_QUERY_THEN_FETCH    與QUERY_THEN_FETCH相同，預期一個初始的散射相伴用來為更準确的score計算配置設定了的term頻率。

DFS_QUERY_AND_FETCH    與QUERY_AND_FETCH相同，預期一個初始的散射相伴用來為更準确的score計算配置設定了的term頻率。

SCAN    在執行了沒有進行任何排序的檢索時執行浏覽。此時将會自動的開始滾動結果集。

COUNT    隻計算結果的數量，也會執行facet。

      (4) setSearchType(String searchType)，與setSearchType(SearchType searchType)類似，差別在于其值為字元串型的SearchType，值可為dfs_query_then_fetch、dfsQueryThenFetch、dfs_query_and_fetch、dfsQueryAndFetch、query_then_fetch、queryThenFetch、query_and_fetch或queryAndFetch；