如何降低通过链接服务器执行的查询的成本
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【中文标题】如何降低通过链接服务器执行的查询的成本【英文标题】：How to reduce cost of the query that is executed through a Linked Server 【发布时间】：2016-03-18 14:08:52 【问题描述】：请看我的执行计划（在SQL10.NG上执行）：
Use [Reporting]
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[sp_WarehouseAttendance_New]
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
---------delete existing warehouse table------------------------------
IF OBJECT_ID('dbo.WarehouseAttendance_New', 'U') IS NOT NULL
TRUNCATE TABLE dbo.WarehouseAttendance_New;
--------Create New Table--------------------------------------------------
---Weeks--------------------------------------------------------------------
With weeks as
(select VDC_week_no, VDC_cal_year, min(VDC_day_date) as WeekCommence
from sql10.ng.dbo.Vdaily_calender
where VDC_avail = 'T'
group by VDC_week_no, VDC_cal_year),
---TTWeeks------------------------------------------------------------------
TTWeeks as
(SELECT VDC_Cal_Year as REMSYear, [VDC_week_no] as WholeYearWeekNo, WeekCommence, ROW_NUMBER() OVER(PARTITION BY vdc_cal_year ORDER BY VDC_week_no) as TermTimeWeekNo
FROM weeks)
---Main---------------------------------------------------------------------
SELECT
s.STYR_Primary_Programme AS PrimaryProgramme,
CASE WHEN s.STYR_Age_end_Aug < 16 THEN '1416' WHEN STYR_Age_end_Aug < 19 THEN '1618' ELSE '19+' END AgeBand,
rg.REGT_Year,
RTRIM(ph.PRPH_ML1) AS PRPH_ML1,
q.GNCD_Description AS [Curriculum Area],
RTRIM(ph.PRPH_ML2) AS Section,
q.GNCD_Description AS Section_Name,
lEFT(q.GNCD_Description, 3) AS Dept,
RTRIM(rg.REGT_Provision_Code) as REGT_Provision_Code,
RTRIM(ph.PRPH_Title) as PRPH_Title,
rg.REGT_Student_ID, STEN_Student_ID, STEN_Funding_Stream,
rs.REGS_Session_No,
RTRIM(rh.REGH_Class_Register) as Class_Register,
RTRIM(rh.REGH_Register_Title) as Register_Title,
CASE WHEN rh.REGH_Day = '1' THEN 'Sunday' WHEN rh.REGH_Day = '2' THEN 'Monday'
WHEN rh.REGH_Day = '3' THEN 'Tuesday' WHEN rh.REGH_Day = '4' THEN 'Wednesday'
WHEN rh.REGH_Day = '5' THEN 'Thursday' WHEN rh.REGH_Day = '6' THEN 'Friday'
WHEN rh.REGH_Day = '7' THEN 'Saturday' END AS Register_Day,
rh.[REGH_Start_Time] as StartTime, rh.[REGH_End_Time] as EndTime,
CASE WHEN (rg.REGT_Provision_Code LIKE '27%'
OR rg.REGT_Provision_Code LIKE 'MA27%' OR
rg.REGT_Provision_Code LIKE 'FS%')
THEN 'FunctionalSkill'
WHEN rg.REGT_Provision_Code LIKE '16%' THEN 'GCSE'
WHEN rg.REGT_Provision_Code LIKE '%/F%' OR
rg.REGT_Provision_Code LIKE '%/D%' OR
rg.REGT_Provision_Code LIKE '%/E%' OR
rg.REGT_Provision_Code LIKE '%/X%' THEN 'Main' ELSE 'Addition' END AS CourseType,
CASE WHEN ISNULL(ra.RGAT_Present,'X') IN ('N', 'Y','X') and rs.REGS_Session_Date<GETDATE()
THEN rs.REGS_Duration - ISNULL(rd.REGD_Mins_Late,0) ELSE 0 END AS Mins_Poss,
CASE WHEN ISNULL(ra.RGAT_Present,'X') = 'Y' AND
rs.REGS_Session_Date<GETDATE() THEN
rs.REGS_Duration - rd.REGD_Mins_Late ELSE 0 END AS Mins_Att,
CASE WHEN ra.RGAT_Present = 'Y' AND rs.REGS_Session_Date<GETDATE() THEN
rd.REGD_Mins_Late ELSE 0 END AS Mins_Late,
rs.[REGS_Session_Date] as Session_Date, TermTimeWeekNo,
rh.REGH_ISN, ph.PRPH_ISN, st.STUD_Surname, st.STUD_Forename_1, rd.REGD_Attendance_Mark,
rg.REGT_start_date, rg.REGT_End_date, WeekCommence,
STFM_LearnFAMCode,
CASE
WHEN STFM_LearnFAMCode=1 THEN '14-15 year old learner is eligible for free meals'
WHEN STFM_LearnFAMCode=2 THEN '16-19 year old learner is eligible for and in receipt of free meals'
ELSE 'N/A'
END AS FreeMealsIndicator,
CASE
WHEN STFM_LearnFAMCode=36 THEN 'Care to Learn (C2L) (EFA funded only)'
WHEN STFM_LearnFAMCode=55 THEN '16-19 Bursary Fund - learner member of a vulnerable group (EFA funded only)'
WHEN STFM_LearnFAMCode=56 THEN '16-19 Bursary Fund - learner awarded discretionary bursary (EFA funded only)'
WHEN STFM_LearnFAMCode=57 THEN 'Residential support (EFA funded only)'
WHEN STFM_LearnFAMCode=58 THEN '19+ Hardship (Skills Funding Agency funded learners only)'
WHEN STFM_LearnFAMCode=59 THEN '20+ Childcare (Skills Funding Agency funded learners only)'
WHEN STFM_LearnFAMCode=60 THEN 'Residential Access Fund (Skills Funding Agency funded learners only)'
WHEN STFM_LearnFAMCode IN (61, 62, 63, 64, 65) THEN 'Unassigned'
ELSE 'N/A'
END AS Bursary,
CASE
WHEN st.STUD_Gender='M' THEN 'Male'
WHEN st.STUD_Gender='F' THEN 'Female'
END AS Gender,
CASE
WHEN st.STUD_Ethnicity= 31 THEN 'White - English / Welsh / Scottish / Northern Irish / British'
WHEN st.STUD_Ethnicity= 32 THEN 'White - Irish'
WHEN st.STUD_Ethnicity= 33 THEN 'White - Gypsy or Irish Traveller'
WHEN st.STUD_Ethnicity= 34 THEN 'White - Any Other White background'
WHEN st.STUD_Ethnicity= 35 THEN 'Mixed / Multiple Ethnic group - White and Black Caribbean'
WHEN st.STUD_Ethnicity= 36 THEN 'Mixed / Multiple Ethnic group - White and Black African'
WHEN st.STUD_Ethnicity= 37 THEN 'Mixed / Multiple Ethnic group - White and Asian'
WHEN st.STUD_Ethnicity= 38 THEN 'Mixed / Multiple Ethnic group - Any Other Mixed / multiple ethnic background'
WHEN st.STUD_Ethnicity= 39 THEN 'Asian / Asian British - Indian'
WHEN st.STUD_Ethnicity= 40 THEN 'Asian/ Asian British - Pakistani'
WHEN st.STUD_Ethnicity= 41 THEN 'Asian / Asian British - Bangladeshi'
WHEN st.STUD_Ethnicity= 42 THEN 'Asian / Asian British - Chinese'
WHEN st.STUD_Ethnicity= 43 THEN 'Asian / Asian British - Any other Asian background'
WHEN st.STUD_Ethnicity= 44 THEN 'Black / African / Caribbean / Black British - African'
WHEN st.STUD_Ethnicity= 45 THEN 'Black / African / Caribbean / Black British - Caribbean'
WHEN st.STUD_Ethnicity= 46 THEN 'Black / African / Caribbean / Black British - Any other Black / African / Caribbean background'
WHEN st.STUD_Ethnicity= 47 THEN 'Other ethnic group - Arab'
WHEN st.STUD_Ethnicity= 98 THEN 'Any Other'
WHEN st.STUD_Ethnicity= 99 THEN 'Not provided'
END AS Ethnicity,
CASE
WHEN g.GNUC_Flag_1 = 1 THEN 'Yes'
WHEN g.GNUC_Flag_1 = 0 THEN 'No'
END AS [Looked After Child],
CASE
WHEN SUB1.GNUC_Type = 'STYR' THEN 'Yes'
WHEN SUB1.GNUC_Type != 'STYR' THEN 'No'
END AS ALS
INTO dbo.WarehouseAttendance_New
FROM
sql10.ng.dbo.REGTrgstudt rg
INNER JOIN
sql10.ng.dbo.REGSrgsessn rs ON rg.REGT_REGH_ISN = rs.REGS_REGH_ISN
INNER JOIN sql10.ng.dbo.Vdaily_calender
ON rs.REGS_Session_Date=VDC_day_date
INNER JOIN TTWeeks on rg.REGT_year=TTWeeks.REMSYear
and VDC_week_no=WholeYearWeekNo and VDC_cal_year=REMSYear
INNER JOIN
sql10.ng.dbo.REGHrghdr rh ON rh.REGH_ISN = rg.REGT_REGH_ISN
INNER JOIN
sql10.ng.dbo.PRphprovisionHeader ph ON rg.REGT_Provision_Code = ph.PRPH_Code
INNER JOIN
sql10.ng.dbo.GNCDgncodes AS ML2 ON ML2.GNCD_General_Code = PRPH_ML2 AND ML2.GNCD_Code_Type = 'M2'
INNER JOIN
sql10.ng.dbo.STEN ON STEN_Student_ID = rg.REGT_Student_ID AND STEN_Provision_Code = rg.REGT_Provision_Code AND
STEN_Provision_Instance = rg.REGT_Provision_Instance
LEFT OUTER JOIN sql10.ng.dbo.STFMLearnerFAM ON STFM_Year = STEN_Year AND STFM_Student_ID = STEN_Student_ID
INNER JOIN
sql10.ng.dbo.STYRstudentYR s ON s.STYR_Student_ID = rg.REGT_Student_ID AND s.STYR_Year = rg.REGT_Year
INNER JOIN (SELECT GNUC_Type, GNUC_Year, GNUC_Entity_ISN FROM sql10.ng.dbo.GNUCustom
WHERE (GNUC_Year IN ('2013', '2014', '2015'))) AS SUB1 ON rg.REGT_Year = SUB1.GNUC_Year
-- AND STYR_ISN = SUB1.GNUC_Entity_ISN
INNER JOIN
(SELECT ACYR_College_Year
FROM sql10.ng.dbo.ACYR
WHERE (ACYR_College_Year in (2015, 2014, 2013, 2012))) AS SUB ON REGT_Year = SUB.ACYR_College_Year
INNER JOIN sql10.ng.dbo.STUDStudent st on s.STYR_Student_ID=st.STUD_Student_ID
INNER JOIN sql10.ng.dbo.GNUCustom g ON STUD_ISN = g.GNUC_Entity_ISN AND g.GNUC_Type = 'STUD'
INNER JOIN sql10.ng.dbo.REGDropin rd ON rg.REGT_REGH_ISN = rd.REGD_REGH_ISN AND rg.REGT_Student_ID = rd.REGD_Student_ID
AND rd.REGD_Session_No = rs.REGS_Session_No
INNER JOIN
sql10.ng.dbo.RGATAttendance ra ON rd.REGD_Attendance_Mark = ra.RGAT_Attendance_Code
INNER JOIN
sql10.ng.dbo.PRPIProvisionInstance AS pit ON pit.PRPI_Code = rg.REGT_Provision_Code
and pit.prpi_instance = REGT_Provision_Instance
INNER JOIN
(SELECT GNCD_General_Code, GNCD_Description
FROM sql10.ng.dbo.GNCDgncodes
WHERE (GNCD_Code_Type = 'M2')) AS q ON q.GNCD_General_Code = RTrim(PRPH_ML2)
COMMIT
END
GO
我在执行存储过程作为将数据填充到表中的作业时遇到了锁定问题，因此我需要知道如何改进查询计划。
谢谢， 阿鲁娜
【问题讨论】：
EXEC('...') AT [SQL10.NG]
清除案例...在程序开始时，将 STFM_LearnFAMCode 和 STUD_Ethnicity 的 ID 和名称放入临时表中，并在您的查询之后加入它们...加入将比案例快得多，因为您可以将索引放在临时表上。这是我要做的第一件事
使用 openquery 与链接服务器数据库对话。
【参考方案1】：
免责声明：我查看了查询，我没有详细阅读。
查询过大。一旦它们达到一定的大小，SQL 优化器就会在生成有效的查询计划时出现问题，而在查询中使用“链接服务器表”只会加剧问题。我会将这个令人难以置信的复杂、过于复杂且通常丑陋的查询分解为多个步骤。
首先对远程服务器或服务器运行数据检索，将返回的数据存储在本地，可能在#temp 表中。 （如果返回的数据很多，请在 #temp 表上建立索引。）接下来，将这些表连接到相关的本地表。
返回的实际列似乎包含嵌入在案例语句中的复杂业务规则。它们可能包含在第二个查询中，或者，如果足够复杂，它们可能会调用第三个查询，第二个查询的结果存储在第二个 #temp 表中。
可以通过 SQL 优化器或通过巧妙的实现更好地优化较小的代码块。太大就是太大。
【讨论】：
【参考方案2】：ALTER PROCEDURE [dbo].[sp_WarehouseAttendance_New]
AS
BEGIN
SET NOCOUNT ON;
...
DECLARE @sql NVARCHAR(MAX) = '
SELECT s.STYR_Primary_Programme AS PrimaryProgramme,
/*....*/
SUB1.GNUC_Type
FROM dbo.REGTrgstudt rg
JOIN dbo.REGSrgsessn rs ON rg.REGT_REGH_ISN = rs.REGS_REGH_ISN
JOIN dbo.Vdaily_calender ON rs.REGS_Session_Date = VDC_day_date
JOIN (
SELECT VDC_Cal_Year AS REMSYear, [VDC_week_no] AS WholeYearWeekNo, WeekCommence, ROW_NUMBER() OVER (PARTITION BY vdc_cal_year ORDER BY VDC_week_no) AS TermTimeWeekNo
FROM (
SELECT VDC_week_no, VDC_cal_year, MIN(VDC_day_date) AS WeekCommence
FROM dbo.Vdaily_calender
WHERE VDC_avail = ''T''
GROUP BY VDC_week_no, VDC_cal_year
) t
) ON rg.REGT_year = TTWeeks.REMSYear
AND VDC_week_no = WholeYearWeekNo
AND VDC_cal_year = REMSYear
JOIN dbo.REGHrghdr rh ON rh.REGH_ISN = rg.REGT_REGH_ISN
JOIN dbo.PRPHProvisionHeader ph ON rg.REGT_Provision_Code = ph.PRPH_Code
JOIN dbo.GNCDgncodes AS ML2 ON ML2.GNCD_General_Code = PRPH_ML2
AND ML2.GNCD_Code_Type = ''M2''
JOIN dbo.STEN ON STEN_Student_ID = rg.REGT_Student_ID
AND STEN_Provision_Code = rg.REGT_Provision_Code
AND STEN_Provision_Instance = rg.REGT_Provision_Instance
LEFT JOIN dbo.STFMLearnerFAM ON STFM_Year = STEN_Year
AND STFM_Student_ID = STEN_Student_ID
INNER JOIN dbo.STYRstudentYR s ON s.STYR_Student_ID = rg.REGT_Student_ID
AND s.STYR_Year = rg.REGT_Year
JOIN (
SELECT GNUC_Type, GNUC_Year, GNUC_Entity_ISN
FROM dbo.GNUCustom
WHERE (GNUC_Year IN (''2013'', ''2014'', ''2015''))
) AS SUB1 ON rg.REGT_Year = SUB1.GNUC_Year
JOIN (
SELECT ACYR_College_Year
FROM dbo.ACYR
WHERE (ACYR_College_Year IN (2015, 2014, 2013, 2012))
) AS SUB ON REGT_Year = SUB.ACYR_College_Year
JOIN dbo.STUDStudent st ON s.STYR_Student_ID = st.STUD_Student_ID
JOIN dbo.GNUCustom g ON STUD_ISN = g.GNUC_Entity_ISN
AND g.GNUC_Type = ''STUD''
JOIN dbo.REGDropin rd ON rg.REGT_REGH_ISN = rd.REGD_REGH_ISN
AND rg.REGT_Student_ID = rd.REGD_Student_ID
AND rd.REGD_Session_No = rs.REGS_Session_No
JOIN dbo.RGATAttendance ra ON rd.REGD_Attendance_Mark = ra.RGAT_Attendance_Code
JOIN dbo.PRPIProvisionInstance AS pit ON pit.PRPI_Code = rg.REGT_Provision_Code
AND pit.prpi_instance = REGT_Provision_Instance
JOIN (
SELECT GNCD_General_Code, GNCD_Description
FROM dbo.GNCDgncodes
WHERE (GNCD_Code_Type = ''M2'')
) AS q ON q.GNCD_General_Code = RTRIM(PRPH_ML2)'
INSERT INTO dbo.WarehouseAttendance_TEMP
EXEC(@sql) AT [sql10.ng]
INSERT INTO dbo.WarehouseAttendance_New
SELECT ...
FROM dbo.WarehouseAttendance_TEMP
END
【讨论】：
【参考方案3】：尝试在存储过程中为 TTWeeks 创建一个表变量。 使用 Common Table 表达式进行 INNER JOIN（如您的情况），每次都会为每条记录计算它，这会在更大程度上影响性能。
类似这样的：
Declare @TTWeeks as table
(
REMSYear int
,WholeYearWeekNo int
,TermTimeWeekNo int
,WeekCommence datetime
)
我同意上面 Philip Kelley 的回答。与巨大的丑陋查询相比，可以更好地优化更小的代码块。
【讨论】：
创建此表后在哪里可以看到？ 像任何其他变量一样在您的存储过程中创建它，然后使用您在 TTWeeks CTE 中使用的查询进行插入。您可以像使用任何其他表一样使用表变量。你应该在你的 sql 中使用 @TTWeeks 而不是 TTWeeks。以上是关于如何降低通过链接服务器执行的查询的成本的主要内容，如果未能解决你的问题，请参考以下文章