Question

我有一个蔚蓝的sql数据库，并从brentozar运行sp_BlitzIndex来识别一些丢失的索引。此sp实际上使用sys.dm_db_missing_index_groups，基本上使用以下查询：

select xxx FROM    sys.dm_db_missing_index_groups ig
JOIN sys.dm_db_missing_index_details id ON ig.index_handle = id.index_handle
JOIN sys.dm_db_missing_index_group_stats gs ON ig.index_group_handle = gs.group_handle

但是，我意识到在创建这些丢失的索引之后，上面的查询仍然会显示与丢失的索引相同的索引，并且到目前为止已经有12个小时了。

医生说：

sys.dm_db_missing_index_groups返回的信息在以下情况下更新查询由查询优化器优化

因此它应该是实时信息，那么为什么这些信息似乎没有更新？

Answer 1

您是否在高速缓存查询计划中发现缺少在查询结果中看不到的索引？如果您在查询计划中没有看到新的缺失索引，则这些DMV应该显示相同的结果。

WITH XMLNAMESPACES
   (DEFAULT 'http://schemas.microsoft.com/sqlserver/2004/07/showplan')

SELECT query_plan,
       n.value('(@StatementText)[1]', 'VARCHAR(4000)') AS sql_text,
       n.value('(//MissingIndexGroup/@Impact)[1]', 'FLOAT') AS impact,
       DB_ID(REPLACE(REPLACE(n.value('(//MissingIndex/@Database)[1]', 'VARCHAR(128)'),'[',''),']','')) AS database_id,
       OBJECT_ID(n.value('(//MissingIndex/@Database)[1]', 'VARCHAR(128)') + '.' +
           n.value('(//MissingIndex/@Schema)[1]', 'VARCHAR(128)') + '.' +
           n.value('(//MissingIndex/@Table)[1]', 'VARCHAR(128)')) AS OBJECT_ID,
       n.value('(//MissingIndex/@Database)[1]', 'VARCHAR(128)') + '.' +
           n.value('(//MissingIndex/@Schema)[1]', 'VARCHAR(128)') + '.' +
           n.value('(//MissingIndex/@Table)[1]', 'VARCHAR(128)')
       AS statement,
       (   SELECT DISTINCT c.value('(@Name)[1]', 'VARCHAR(128)') + ', '
           FROM n.nodes('//ColumnGroup') AS t(cg)
           CROSS APPLY cg.nodes('Column') AS r(c)
           WHERE cg.value('(@Usage)[1]', 'VARCHAR(128)') = 'EQUALITY'
           FOR  XML PATH('')
       ) AS equality_columns,
        (  SELECT DISTINCT c.value('(@Name)[1]', 'VARCHAR(128)') + ', '
           FROM n.nodes('//ColumnGroup') AS t(cg)
           CROSS APPLY cg.nodes('Column') AS r(c)
           WHERE cg.value('(@Usage)[1]', 'VARCHAR(128)') = 'INEQUALITY'
           FOR  XML PATH('')
       ) AS inequality_columns,
       (   SELECT DISTINCT c.value('(@Name)[1]', 'VARCHAR(128)') + ', '
           FROM n.nodes('//ColumnGroup') AS t(cg)
           CROSS APPLY cg.nodes('Column') AS r(c)
           WHERE cg.value('(@Usage)[1]', 'VARCHAR(128)') = 'INCLUDE'
           FOR  XML PATH('')
       ) AS include_columns
INTO #MissingIndexInfo
FROM
(
   SELECT query_plan
   FROM (
           SELECT DISTINCT plan_handle
           FROM sys.dm_exec_query_stats WITH(NOLOCK)
         ) AS qs
       OUTER APPLY sys.dm_exec_query_plan(qs.plan_handle) tp
   WHERE tp.query_plan.exist('//MissingIndex')=1
) AS tab (query_plan)
CROSS APPLY query_plan.nodes('//StmtSimple') AS q(n)
WHERE n.exist('QueryPlan/MissingIndexes') = 1;

-- Trim trailing comma from lists
UPDATE #MissingIndexInfo
SET equality_columns = LEFT(equality_columns,LEN(equality_columns)-1),
   inequality_columns = LEFT(inequality_columns,LEN(inequality_columns)-1),
   include_columns = LEFT(include_columns,LEN(include_columns)-1);

SELECT *
FROM #MissingIndexInfo;

DROP TABLE #MissingIndexInfo;

为什么Azure SQL的sys.dm_db_missing_index_groups无法更新？

1 个答案: