这是个有趣的问题。过去一周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情况统计信息。
从未出现在使用统计表中的索引
然而,许多索引根本不会出现在该表中。 David Andres 发布的查询列出了此案例的所有索引。我对其进行了一些更新以忽略主键,即使它们从未使用过,也可能不应该删除它们。我还加入了 dm_db_index_physical_stats 表以获取其他信息,包括页计数、总索引大小和碎片百分比。有趣的是,此查询返回的索引似乎没有显示在索引使用情况统计的 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
确实出现在使用情况统计表中但从未使用过的索引
还有其他索引确实出现在 dm_db_index_usage_stats 表中,但从未用于用户查找、扫描或查找。该查询将识别属于该类别的索引。顺便说一句,与从其他查询返回的索引不同,此查询中返回的索引可以通过索引使用统计信息在 SQL 报告上进行验证。
我添加了“最小页数”,使我能够首先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,一旦索引被确定为候选人对于移除,仍应仔细考虑,以确保这样做是一个好的决定。
有关更多信息,请参阅识别 SQL Server 数据库中未使用的索引 http://www.foliotek.com/devblog/identifying-unused-indexes-in-a-sql-server-database/