如何诊断缓慢/不一致的SQL Server查询？

Question

运行Windows Server 2012，Hyper-V，SQL Server 2012主动/被动故障转移群集，具有两个8处理器，60GB节点，单个实例，300个数据库。此查询会产生不一致的结果，运行时间在10到30秒之间。

DECLARE @OrgID           BigInt = 780246
DECLARE @ActiveOnly      Bit = 0
DECLARE @RestrictToOrgID Bit = 0;

WITH og (OrgID, GroupID) AS
  (
  SELECT ID, ID FROM Common.com.Organizations WHERE ISNULL(ParentID, 0) <> ID 
  UNION ALL
  SELECT o.ID, og.GroupID FROM Common.com.Organizations o JOIN og ON og.OrgID = o.ParentID
  )

   SELECT e.*, v.Type AS VendorType, v.F1099, v.F1099Type, v.TaxID, v.TaxPercent,
          v.ContactName, v.ContactPhone, v.ContactEMail, v.DistrictWide, 
          a.*
     FROM og
     JOIN books.Organizations           bo ON  bo.CommonID = og.OrgID
     JOIN books.Organizations           po ON  po.CommonID = og.GroupID
     JOIN books.Entities                e  ON   e.OrgID    = po.ID
     JOIN Vendors                       v  ON   v.ID       =  e.ID 
                                           AND (e.OrgID    = bo.ID OR v.DistrictWide = 1)
LEFT JOIN Addresses                     a  ON   a.ID       =  e.AddressID
    WHERE bo.ID = @OrgID
      AND (@ActiveOnly      = 0 OR e.Active = 1)
      AND (@RestrictToOrgID = 0 OR e.OrgID  = @OrgID)
 ORDER BY e.EntityName

用LEFT JOIN Addresses替换JOIN Addresses

     JOIN Addresses                     a  ON   a.ID       =  e.AddressID
    WHERE bo.ID = @OrgID
      AND (@ActiveOnly      = 0 OR e.Active = 1)
      AND (@RestrictToOrgID = 0 OR e.OrgID  = @OrgID)
 ORDER BY e.EntityName

或者将从Addresses中选择的列的长度减少到小于100个字节

   SELECT e.*, v.Type AS VendorType, v.F1099, v.F1099Type, v.TaxID, v.TaxPercent,
          v.ContactName, v.ContactPhone, v.ContactEMail, v.DistrictWide, 
          a.Fax

将执行时间缩短到约0.5秒。

此外，使用SELECT DISTINCT并将books.Entities加入Vendors

   SELECT DISTINCT e.*, v.Type AS VendorType, v.F1099, v.F1099Type, v.TaxID, v.TaxPercent,
          v.ContactName, v.ContactPhone, v.ContactEMail, v.DistrictWide, 
          a.*
     FROM og
     JOIN books.Organizations           bo ON  bo.CommonID = og.OrgID
     JOIN books.Organizations           po ON  po.CommonID = og.GroupID
     JOIN Vendors                       v  
     JOIN books.Entities                e  ON   v.ID       =  e.ID 
                                           ON   e.OrgID    = bo.ID OR (e.OrgID = po.ID AND v.DistrictWide = 1)

将时间缩短到约0.75秒。

摘要

这些条件表明SQL Server实例中存在某种资源限制导致这些不稳定的结果，我不知道如何进行诊断。如果我将有问题的数据库复制到运行SQL Server 2012的笔记本电脑上，则问题不存在。我可以继续改变SQL并希望最好，但我更愿意找到更明确的解决方案。

任何建议表示赞赏。

更新2/27/18

未修改查询的执行计划显示针对地址表的聚集索引搜索作为问题。

将从Addresses中选择的列的长度减少到小于100个字节

   SELECT e.*, v.Type AS VendorType, v.F1099, v.F1099Type, v.TaxID, v.TaxPercent,
          v.ContactName, v.ContactPhone, v.ContactEMail, v.DistrictWide, 
          a.Fax

使用聚集索引扫描替换聚集索引搜索以检索a.Fax和哈希匹配以将此值连接到结果。

Addresses表主键创建如下：

   ALTER TABLE dbo.Addresses 
ADD CONSTRAINT PK_Addresses PRIMARY KEY CLUSTERED (ID ASC)
          WITH (PAD_INDEX = OFF, 
                STATISTICS_NORECOMPUTE = OFF, 
                SORT_IN_TEMPDB         = OFF, 
                IGNORE_DUP_KEY         = OFF, 
                ONLINE                 = OFF, 
                ALLOW_ROW_LOCKS        = ON, 
                ALLOW_PAGE_LOCKS       = ON) 
            ON  PRIMARY

每天根据需要对该索引进行碎片整理和优化。

到目前为止，我找不到为什么Clustered Index Seek为查询增加了这么多时间。

Answer 1

好的，就像往常一样，没有一个问题，而是两个问题。这是复杂问题分析可能导致错误结论的一个例子。

最主要的问题是递归CTE og，它返回一个数据透视表，给出组织之间的父/子关系。但是，对执行计划的分析似乎表明问题是优化器中的某种故障与从左连接表返回的数据量有关。这可能完全是由于我无法正确分析执行计划，但在这些情况下SQL Server 2012 SP4如何创建执行计划似乎存在一些问题。

虽然在我们的生产服务器上更为重要，但SQL Server优化递归CTE的问题在我的localhost（运行2012 SP4）和登台服务器（运行SP2）上都很明显。但需要进一步分析和猜测才能看到它。

解决方案

我用一个数据透视表替换了递归CTE，并在Organizations表中添加了一个触发器来维护它。

USE Common
GO

CREATE VIEW com.OrganizationGroupsCTE
AS
  WITH cte (OrgID, GroupID) AS
    (
    SELECT ID, ID FROM com.Organizations WHERE ISNULL(ParentID, 0) <> ID 
    UNION ALL
    SELECT o.ID, cte.GroupID FROM com.Organizations o JOIN cte ON cte.OrgID = o.ParentID
    )

  SELECT OrgID, GroupID FROM cte
GO

CREATE TABLE com.OrganizationGroups 
  (
  OrgID   BIGINT, 
  GroupID BIGINT
  )

INSERT com.OrganizationGroups 
SELECT OrgID, GroupID 
  FROM com.OrganizationGroupsCTE
GO

CREATE TRIGGER TR_OrganizationGroups ON com.Organizations AFTER INSERT,UPDATE,DELETE
AS
  DELETE og 
    FROM com.OrganizationGroups og 
    JOIN deleted                d   ON d.ID IN (og.groupID, og.orgID);

  INSERT com.OrganizationGroups 
  SELECT orgID, groupID 
    FROM inserted               i 
    JOIN OrganizationGroupsCTE  cte ON i.ID IN (cte.orgID, cte.groupID)
GO

修改查询以使用数据透视表后，

   SELECT e.*, v.Type AS VendorType, v.F1099, v.F1099Type, v.TaxID, v.TaxPercent,
          v.ContactName, v.ContactPhone, v.ContactEMail, v.DistrictWide, 
          a.*
     FROM Common.com.OrganizationGroups og
     JOIN books.Organizations           bo ON  bo.CommonID = og.OrgID
     JOIN books.Organizations           po ON  po.CommonID = og.GroupID
     JOIN books.Entities                e  ON   e.OrgID    = po.ID
     JOIN Vendors                       v  ON   v.ID       =  e.ID 
                                           AND (e.OrgID    = bo.ID OR v.DistrictWide = 1)
LEFT JOIN Addresses                     a  ON   a.ID       =  e.AddressID
    WHERE bo.ID = @OrgID
      AND (@ActiveOnly      = 0 OR e.Active = 1)
      AND (@RestrictToOrgID = 0 OR e.OrgID  = @OrgID)
 ORDER BY e.EntityName

在所有三种环境中，SQL Server性能都得到了改进和一致。现在已经消除了生产服务器上的问题。