mysql - 如何优化 Entity Framework 查询

Question

我正在使用 Linq-To-Entities 执行查询，该查询仅返回 947 行但运行时间为 18 秒。我已经完成了一个“ToTraceString”来获取底层的 sql 并直接在数据库上运行相同的东西并获得相同的时间。

我使用了调优顾问并创建了几个索引，尽管影响很小。

查看查询执行计划，有几个嵌套循环占用了 95% 的时间，但这些循环已经在处理索引了？

有没有人对如何强制对 EF 查询进行某些优化有任何想法？

编辑:提供额外信息

三个表的基本ER图如下:

People >----People_Event_Link ----< Events
P_ID        P_ID                    E_ID
            E_ID

我正在运行的 linq 旨在为特定的人(使用 P_ID)取回所有事件:

        var query = from ev in genesisContext.Events
                    join pe in genesisContext.People_Event_Link
                    on ev equals pe.Event
                    where pe.P_ID == key
                    select ev;
        return query;

这是生成的 SQL(深呼吸!):

SELECT 
1 AS [C1], 
[Extent1].[E_ID] AS [E_ID], 
[Extent1].[E_START_DATE] AS [E_START_DATE], 
[Extent1].[E_END_DATE] AS [E_END_DATE], 
[Extent1].[E_COMMENTS] AS [E_COMMENTS], 
[Extent1].[E_DATE_ADDED] AS [E_DATE_ADDED], 
[Extent1].[E_RECORDED_BY] AS [E_RECORDED_BY], 
[Extent1].[E_DATE_UPDATED] AS [E_DATE_UPDATED], 
[Extent1].[E_UPDATED_BY] AS [E_UPDATED_BY], 
[Extent1].[ET_ID] AS [ET_ID], 
[Extent1].[L_ID] AS [L_ID]
FROM  [dbo].[Events] AS [Extent1]
INNER JOIN [dbo].[People_Event_Link] AS [Extent2] ON  EXISTS (SELECT 
    1 AS [C1]
    FROM    ( SELECT 1 AS X ) AS [SingleRowTable1]
    LEFT OUTER JOIN  (SELECT 
        [Extent3].[E_ID] AS [E_ID]
        FROM [dbo].[Events] AS [Extent3]
        WHERE [Extent2].[E_ID] = [Extent3].[E_ID] ) AS [Project1] ON 1 = 1
    LEFT OUTER JOIN  (SELECT 
        [Extent4].[E_ID] AS [E_ID]
        FROM [dbo].[Events] AS [Extent4]
        WHERE [Extent2].[E_ID] = [Extent4].[E_ID] ) AS [Project2] ON 1 = 1
    WHERE ([Extent1].[E_ID] = [Project1].[E_ID]) OR (([Extent1].[E_ID] IS NULL) AND ([Project2].[E_ID] IS NULL))
)
WHERE [Extent2].[P_ID] = 291

Answer 1

是的。重写 LINQ 查询。大多数 LINQ to Entities 查询都可以用多种不同的方式编写，并且会以不同的方式转换为 SQL。由于您既没有显示 LINQ 也没有显示 SQL 也没有显示查询计划，所以我只能说这些。

不过，您很聪明，尝试直接执行 SQL。查询编译也可能需要时间，但您已通过确定 SQL 占所有测量时间来排除这种情况。

尝试:

    var query = from pe in genesisContext.People_Event_Link
                where pe.P_ID == key
                from ev in pe.Event // presuming one to many
                select ev;

或者如果 pe.Event 是一对一的:

    var query = from pe in genesisContext.People_Event_Link
                where pe.P_ID == key
                select pe.Event;

    return query;