sql-server - 如何监视和查找 sql 数据库中未使用的索引

Question

我想监视 sql 数据库的索引使用情况，以便找到未使用的索引然后删除它们。如何最有效地监控索引使用情况？哪些脚本可能有用？

（我知道这个关于识别未使用对象的问题，但这仅适用于 sql server 的当前运行。我想在一段时间内监控索引使用情况......）

Answer 1

这是个有趣的问题。在过去的一周里，我一直在研究同样的问题。有一个名为 dm_db_index_usage_stats 的系统表，其中包含索引的使用统计信息。

从未出现在使用统计表中的索引

然而，很多索引根本就没有出现在这个表中。David Andres 发布的查询列出了此案例的所有索引。我已经对其进行了一些更新以忽略主键，即使它们从未使用过，它们也可能不应该被删除。我还加入了 dm_db_index_physical_stats 表以获取其他信息，包括页数、总索引大小和碎片百分比。一个有趣的注意事项是，此查询返回的索引似乎没有出现在索引使用统计的 SQL 报告中。

DECLARE @dbid INT
SELECT @dbid = DB_ID(DB_NAME())

SELECT  Databases.Name AS [Database],
        Objects.NAME AS [Table],
        Indexes.NAME AS [Index],
        Indexes.INDEX_ID,
        PhysicalStats.page_count as [Page Count],
        CONVERT(decimal(18,2), PhysicalStats.page_count * 8 / 1024.0) AS [Total Index Size (MB)],
        CONVERT(decimal(18,2), PhysicalStats.avg_fragmentation_in_percent) AS [Fragmentation (%)]
FROM SYS.INDEXES Indexes
    INNER JOIN SYS.OBJECTS Objects ON Indexes.OBJECT_ID = Objects.OBJECT_ID
    LEFT JOIN sys.dm_db_index_physical_stats(@dbid, null, null, null, null) PhysicalStats
        on PhysicalStats.object_id = Indexes.object_id and PhysicalStats.index_id = indexes.index_id
    INNER JOIN sys.databases Databases
        ON Databases.database_id = PhysicalStats.database_id
WHERE OBJECTPROPERTY(Objects.OBJECT_ID,'IsUserTable') = 1
    AND Indexes.type = 2    -- Nonclustered indexes
    AND   Indexes.INDEX_ID NOT IN (
            SELECT UsageStats.INDEX_ID
            FROM SYS.DM_DB_INDEX_USAGE_STATS UsageStats
            WHERE UsageStats.OBJECT_ID = Indexes.OBJECT_ID
                AND   Indexes.INDEX_ID = UsageStats.INDEX_ID
                AND   DATABASE_ID = @dbid)
ORDER BY PhysicalStats.page_count DESC,
         Objects.NAME,
         Indexes.INDEX_ID,
         Indexes.NAME ASC

确实出现在使用统计表中但从未使用过的索引

dm_db_index_usage_stats 表中确实出现了其他索引，但从未用于用户查找、扫描或查找。此查询将识别属于此类别的索引。顺便说一句，与从其他查询返回的索引不同，在此查询中返回的索引可以通过索引使用统计在 SQL 报告中进行验证。

我添加了一个最小页数，它允许我最初关注并删除占用大量存储空间的未使用索引。

DECLARE @MinimumPageCount int
SET @MinimumPageCount = 500

SELECT  Databases.name AS [Database], 
        Indexes.name AS [Index],
        Objects.Name AS [Table],                    
        PhysicalStats.page_count as [Page Count],
        CONVERT(decimal(18,2), PhysicalStats.page_count * 8 / 1024.0) AS [Total Index Size (MB)],
        CONVERT(decimal(18,2), PhysicalStats.avg_fragmentation_in_percent) AS [Fragmentation (%)],
        ParititionStats.row_count AS [Row Count],
        CONVERT(decimal(18,2), (PhysicalStats.page_count * 8.0 * 1024) / ParititionStats.row_count) AS [Index Size/Row (Bytes)]
FROM sys.dm_db_index_usage_stats UsageStats
    INNER JOIN sys.indexes Indexes
        ON Indexes.index_id = UsageStats.index_id
            AND Indexes.object_id = UsageStats.object_id
    INNER JOIN sys.objects Objects
        ON Objects.object_id = UsageStats.object_id
    INNER JOIN SYS.databases Databases
        ON Databases.database_id = UsageStats.database_id       
    INNER JOIN sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL, NULL, NULL) AS PhysicalStats
        ON PhysicalStats.index_id = UsageStats.Index_id 
            and PhysicalStats.object_id = UsageStats.object_id
    INNER JOIN SYS.dm_db_partition_stats ParititionStats
        ON ParititionStats.index_id = UsageStats.index_id
            and ParititionStats.object_id = UsageStats.object_id        
WHERE UsageStats.user_scans = 0
    AND UsageStats.user_seeks = 0
    AND UsageStats.user_lookups = 0
    AND PhysicalStats.page_count > @MinimumPageCount    -- ignore indexes with less than 500 pages of memory
    AND Indexes.type_desc != 'CLUSTERED'                -- Exclude primary keys, which should not be removed    
ORDER BY [Page Count] DESC

我希望这有帮助。

最后的想法

当然，一旦索引被确定为删除的候选者，仍应仔细考虑以确保这样做是一个好的决定。

有关详细信息，请参阅识别 SQL Server 数据库中未使用的索引

Answer 2

目前（从 SQL Server 2005 - 2008 开始）SQL 索引统计信息仅保存在内存中，因此如果您希望在重新启动和数据库分离时保留这些信息，您必须自己完成一些工作。

我通常做的是创建一个每天运行的作业，并将在sys.dm_db_index_usage_stats表中找到的信息快照到我为相关数据库创建的自定义表中。

在支持持久索引使用统计的未来版本的 SQL 之前，这似乎工作得很好。

Answer 3

把这只小狗从http://blog.sqlauthority.com/2008/02/11/sql-server-2005-find-unused-indexes-of-current-database/上拉下来。请注意，这适用于 2005 年及更高版本。关键是JOIN系统SYS.DM_DB_INDEX_USAGE_STATS表。

USE AdventureWorks
GO
DECLARE @dbid INT
SELECT @dbid = DB_ID(DB_NAME())
SELECT OBJECTNAME = OBJECT_NAME(I.OBJECT_ID),
                    INDEXNAME = I.NAME,
                    I.INDEX_ID
FROM SYS.INDEXES I
JOIN SYS.OBJECTS O ON I.OBJECT_ID = O.OBJECT_ID
WHERE OBJECTPROPERTY(O.OBJECT_ID,'IsUserTable') = 1
AND   I.INDEX_ID NOT IN (

SELECT S.INDEX_ID
FROM SYS.DM_DB_INDEX_USAGE_STATS S
WHERE S.OBJECT_ID = I.OBJECT_ID
AND   I.INDEX_ID = S.INDEX_ID
AND   DATABASE_ID = @dbid)
ORDER BY OBJECTNAME,
         I.INDEX_ID,
         INDEXNAME ASC
GO

Answer 4

我在这里调整了 John Pasquet 的查询：Identifying Unused Indexes in a SQL Server Database to return index used 10 or less time, union the results that are not in the usage stats tables, exclude heap index and unique constraint or primary key index, 最后排除零页索引。

小心这个查询的结果——最好在生产环境中使用索引实际上以你期望的方式使用。如果您查询具有重建或删除/重新创建索引的数据库或最近的数据库备份，您可能会得到误报（通常会使用但不是因为特殊情况的索引）。在测试或开发环境中使用来决定是否删除索引是不安全的。正如 Nernian 所说，此查询仅确定要删除的候选对象，供您仔细考虑。

USE [DatabaseName]

DECLARE @MinimumPageCount int
SET @MinimumPageCount = 500

DECLARE @dbid INT
SELECT @dbid = DB_ID(DB_NAME())

-- GET UNUSED INDEXES THAT APPEAR IN THE INDEX USAGE STATS TABLE

SELECT  
    Databases.name AS [Database]
    ,object_name(Indexes.object_id) AS [Table]
    ,Indexes.name AS [Index]
    ,PhysicalStats.page_count as [Page Count]
    ,CONVERT(decimal(18,2), PhysicalStats.page_count * 8 / 1024.0) AS [Total Index Size (MB)]
    ,CONVERT(decimal(18,2), PhysicalStats.avg_fragmentation_in_percent) AS [Fragmentation (%)]
    ,ParititionStats.row_count AS [Row Count]
    ,CONVERT(decimal(18,2), (PhysicalStats.page_count * 8.0 * 1024) / ParititionStats.row_count) AS [Index Size Per Row (Bytes)]
    ,1 AS [Appears In Usage Stats Table]

FROM sys.dm_db_index_usage_stats UsageStats

INNER JOIN sys.indexes Indexes
    ON Indexes.index_id = UsageStats.index_id AND Indexes.object_id = UsageStats.object_id

INNER JOIN SYS.databases Databases
    ON Databases.database_id = UsageStats.database_id

INNER JOIN sys.dm_db_index_physical_stats (DB_ID(),NULL,NULL,NULL,NULL) AS PhysicalStats
    ON PhysicalStats.index_id = UsageStats.Index_id AND PhysicalStats.object_id = UsageStats.object_id

INNER JOIN SYS.dm_db_partition_stats ParititionStats
    ON ParititionStats.index_id = UsageStats.index_id AND ParititionStats.object_id = UsageStats.object_id

WHERE 
    UsageStats.user_scans <= 10
    AND UsageStats.user_seeks <= 10
    AND UsageStats.user_lookups <= 10

    -- exclude heap indexes
    AND Indexes.name IS NOT NULL

    -- ignore indexes with less than a certain number of pages of memory
    AND PhysicalStats.page_count > @MinimumPageCount

    -- Exclude primary keys, which should not be removed
    AND Indexes.is_primary_key = 0

    -- ignore unique constraints - those shouldn't be removed 
    AND Indexes.is_unique_constraint = 0 
    AND Indexes.is_unique = 0

UNION ALL 
(
    -- GET UNUSED INDEXES THAT DO **NOT** APPEAR IN THE INDEX USAGE STATS TABLE

    SELECT  
        Databases.Name AS [Database]
        ,Objects.NAME AS [Table]
        ,Indexes.NAME AS [Index]
        ,PhysicalStats.page_count as [Page Count]
        ,CONVERT(decimal(18,2), PhysicalStats.page_count * 8 / 1024.0) AS [Total Index Size (MB)]
        ,CONVERT(decimal(18,2), PhysicalStats.avg_fragmentation_in_percent) AS [Fragmentation (%)]
        ,-1 AS [Row Count]
        ,-1 AS [Index Size Per Row (Bytes)]
        ,0 AS [Appears In Usage Stats Table]

    FROM SYS.INDEXES Indexes

    INNER JOIN SYS.OBJECTS Objects 
        ON Indexes.OBJECT_ID = Objects.OBJECT_ID

    LEFT JOIN sys.dm_db_index_physical_stats(@dbid, null, null, null, null) PhysicalStats
        ON PhysicalStats.object_id = Indexes.object_id AND PhysicalStats.index_id = indexes.index_id

    INNER JOIN sys.databases Databases
        ON Databases.database_id = PhysicalStats.database_id

    WHERE 
        Objects.type = 'U' -- Is User Table

        -- exclude heap indexes
        AND Indexes.name IS NOT NULL

        -- exclude empty tables
        AND PhysicalStats.page_count <> 0

        -- Exclude primary keys, which should not be removed
        AND Indexes.is_primary_key = 0

        -- ignore unique constraints - those shouldn't be removed 
        AND Indexes.is_unique_constraint = 0 
        AND Indexes.is_unique = 0

        AND Indexes.INDEX_ID NOT IN 
        (
            SELECT UsageStats.INDEX_ID
            FROM SYS.DM_DB_INDEX_USAGE_STATS UsageStats
            WHERE 
                UsageStats.OBJECT_ID = Indexes.OBJECT_ID
                AND Indexes.INDEX_ID = UsageStats.INDEX_ID
                AND DATABASE_ID = @dbid
        )
)

ORDER BY [Table] ASC, [Total Index Size (MB)] DESC

Answer 5

你应该看看 Brent Ozars sp_BlitzIndex。此存储过程列出了其他未使用的索引。它在报告中列出了这些疾病。对于每个条目，都会给出一个 URL，该 URL 解释了要查找的内容以及如何处理问题。