统计--过滤(筛选)索引的统计信息过期问题测试2

时间：2014-11-08 13:17:44 阅读：278 评论：0 收藏：0 [点我收藏+]

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在上次的文章统计--过滤(筛选)索引的统计信息过期问题测试中，遗留一个问题，当更新行数满足统计自动更新条件是，什么样的查询会触发自动更新呢？

受林勇桦的指点，找到以下2个跟踪标志：

9204 – 打印出被加载的统计信息（With this enabled, we get a report of statistics objects which are considered ‘interesting’ by the query optimizer when compiling, or recompiling the query in question. For potentially useful statistics, just the header is loaded.）

9292 – 打印出从元数据中得到的统计信息的头信息（With this enabled, we see the ‘interesting’ statistics which end up being fully loaded and used to produce cardinality and distribution estimates for some plan alternative or other. Again, this only happens when a plan is compiled or recompiled – not when a plan is retrieved from cache.）

使用这两个标志，我们可以执行时知道使用了那些统计信息

准备测试数据

--创建表,并插入5000行数据
SELECT TOP(5000) 
IDENTITY(INT,1,1) AS ID,
* 
INTO TB001
FROM SYS.all_columns
GO
--创建聚簇索引
CREATE CLUSTERED INDEX IDX_ID
ON TB001(ID)
GO
--创建过滤索引
CREATE INDEX IDX_COLUMNID
ON TB001(object_id)
WHERE Column_id<3
GO
--再导入25000行数据
INSERT INTO TB001
SELECT TOP(5000) 
* 
FROM SYS.all_columns
GO 5
--更新统计信息
UPDATE STATISTICS TB001
GO
INSERT INTO TB001
SELECT TOP(5000) 
* 
FROM SYS.all_columns
GO 4

开启跟踪标志并执行查询

DBCC FREEPROCCACHE()
GO
DBCC TRACEON(3604, 9292, 9204)
GO
--执行使用过滤索引但不能触发自动更新的查询
SELECT COUNT(1) FROM TB001
WHERE Column_id<3

Stats header loaded: DbName: TestDB01, ObjName: TB001, IndexId: 3, ColumnName: column_id, EmptyTable: FALSE

Stats loaded: DbName: TestDB01, ObjName: TB001, IndexId: 3, ColumnName: column_id, EmptyTable: FALSE

我们发现以上查询加载了IndexID:3的统计信息（并不存在IndexId=3的索引），该统计信息在查询时被自动生成

开始第二轮测试：

DBCC FREEPROCCACHE()
GO
DBCC TRACEON(3604, 9292, 9204)
GO

--执行使用过滤索引且能触发自动更新的查询
SELECT TOP(1) object_id,COUNT(1)
FROM TB001
WHERE Column_id<3
GROUP BY object_id 
ORDER BY COUNT(1) DESC

Stats header loaded: DbName: TestDB01, ObjName: TB001, IndexId: 3, ColumnName: column_id, EmptyTable: FALSE

Stats loaded: DbName: TestDB01, ObjName: TB001, IndexId: 3, ColumnName: column_id, EmptyTable: FALSE

Stats header loaded: DbName: TestDB01, ObjName: TB001, IndexId: 4, ColumnName: object_id, EmptyTable: FALSE

Stats loaded: DbName: TestDB01, ObjName: TB001, IndexId: 4, ColumnName: object_id, EmptyTable: FALSE

Filtered stats header loaded: DbName: TestDB01, ObjName: TB001, IndexId: 2, ColumnName: object_id, Expr: ([Column_id]<(3)),  EmptyTable: FALSE

Filtered stats loaded: DbName: TestDB01, ObjName: TB001, IndexId: 2, ColumnName: object_id, Expr: ([Column_id]<(3)),  EmptyTable: FALSE