谜团：在SQL表中慢速删除

Question

我有一个包含29列和3000-4000行的SQL表。它有一些空间领域（2几何和1地理），但没有什么特别的。

在生产和开发环境中，从此表中删除单行现在大约需要1000毫秒。

Delete from AdminDivisions 
where AdminDivisionID=(Select top 1 AdminDivisionID from AdminDivisions)

这是我尝试过的（在开发环境中）：

• 我已经对表进行了克隆，并精心重新创建了所有触发器，外键，约束和索引。从克隆中删除行是即时的。

   Delete from _ad
   where AdminDivisionID=(Select top 1 AdminDivisionID from AdminDivisions)
  

• 我删除了原始表中的所有触发器，外键，约束和索引。从精简表中删除一行仍然需要大约1000毫秒。

我接下来可以尝试什么？

---

更新1

这是执行计划（full size here）。引用此表的是FK - 以及表自己的PK索引。还不确定从哪里开始。

更新2

@Martin：这是SET STATISTICS IO ON的输出：

Table 'Instances'. Scan count 1, logical reads 12, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Locations'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'AwardsAdminDivisionsXtab'. Scan count 1, logical reads 3, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'IndicatorResultComments'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'IndicatorResults'. Scan count 1, logical reads 35958, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Transactions'. Scan count 1, logical reads 155, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LogicCheckViolations'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'AdminDivisions'. Scan count 1, logical reads 14, physical reads 0, read-ahead reads 0, lob logical reads 1, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 1, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'AspNet_SqlCacheTablesForChangeNotification'. Scan count 0, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

Answer 1

只是猜测因为我没有足够的信息：

1. 也许目标表（AdminDivisions）是父表，并且有一个FK引用了AdminDivisions内的PK或UQ（唯一键）和
2. 此FK具有ON DELETE CASCADE选项和
3. 此FK未编入索引。

示例：

CREATE TABLE dbo.ParentTable(
    ID INT IDENTITY(1,1) PRIMARY KEY,
    Name NVARCHAR(50) NOT NULL
);
GO
CREATE TABLE dbo.ChildTable(
    ID INT IDENTITY(1,1) PRIMARY KEY,
    ParentID INT NOT NULL 
        REFERENCES dbo.ParentTable(ID) ON DELETE CASCADE
);
GO
DELETE dbo.ParentTable
WHERE ID = 1;       

DELETE dbo.ParentTable ...语句之前在dbo.ChildTable(ParentID)上创建索引的执行计划：

在DELETE dbo.ParentTable ...（dbo.ChildTable(ParentID)）上创建索引之后CREATE INDEX IX1 ON dbo.ChildTable(ParentID);语句的执行计划：