我们有一个客户网站,其中一台服务器上有一个50Gb的SQL 2012数据库和100+ Gb的RAM。
由于应用程序被使用时,SQL服务器会将数据库缓存到内存中,但性能提升发生在第二次运行查询时,而不是第一次。
为了尝试最大化第一次运行查询时的缓存命中率,我们编写了一个过程,遍历整个数据库中每个表的每个索引,运行以下代码:
SELECT * INTO #Cache
FROM ' + @tablename + ' WITH (INDEX (' + @indexname + '))'
为了尽可能地强制读取尽可能多的数据,我们计划每15分钟运行一次,并且通常表现良好。
不讨论其他瓶颈、硬件规格、查询计划或查询优化,是否有人有更好的想法来完成同样的任务呢?
更新:
感谢提供的建议。已将“INTO #Cache”移除,并进行了测试,但并没有对填充缓冲区产生影响。
添加:我选择仅从索引中选择键,而不是选择所有内容。显然,这样更加直接,速度也更快。
添加:还要读取和缓存约束索引。
以下是当前的代码:(希望对其他人有用)
CREATE VIEW _IndexView
as
-- Easy way to access sysobject and sysindex data
SELECT
so.name as tablename,
si.name as indexname,
CASE si.indid WHEN 1 THEN 1 ELSE 0 END as isClustered,
CASE WHEN (si.status & 2)<>0 then 1 else 0 end as isUnique,
dbo._GetIndexKeys(so.name, si.indid) as Keys,
CONVERT(bit,CASE WHEN EXISTS (SELECT * FROM sysconstraints sc WHERE object_name(sc.constid) = si.name) THEN 1 ELSE 0 END) as IsConstraintIndex
FROM sysobjects so
INNER JOIN sysindexes si ON so.id = si.id
WHERE (so.xtype = 'U')--User Table
AND ((si.status & 64) = 0) --Not statistics index
AND ( (si.indid = 0) AND (so.name <> si.name) --not a default clustered index
OR
(si.indid > 0)
)
AND si.indid <> 255 --is not a system index placeholder
UNION
SELECT
so.name as tablename,
si.name as indexname,
CASE si.indid WHEN 1 THEN 1 ELSE 0 END as isClustered,
CASE WHEN (si.status & 2)<>0 then 1 else 0 end as isUnique,
dbo._GetIndexKeys(so.name, si.indid) as Keys,
CONVERT(bit,0) as IsConstraintIndex
FROM sysobjects so
INNER JOIN sysindexes si ON so.id = si.id
WHERE (so.xtype = 'V')--View
AND ((si.status & 64) = 0) --Not statistics index
GO
CREATE PROCEDURE _CacheTableToSQLMemory
@tablename varchar(100)
AS
BEGIN
DECLARE @indexname varchar(100)
DECLARE @xtype varchar(10)
DECLARE @SQL varchar(MAX)
DECLARE @keys varchar(1000)
DECLARE @cur CURSOR
SET @cur = CURSOR FOR
SELECT v.IndexName, so.xtype, v.keys
FROM _IndexView v
INNER JOIN sysobjects so ON so.name = v.tablename
WHERE tablename = @tablename
PRINT 'Caching Table ' + @Tablename
OPEN @cur
FETCH NEXT FROM @cur INTO @indexname, @xtype, @keys
WHILE (@@FETCH_STATUS = 0)
BEGIN
PRINT ' Index ' + @indexname
--BEGIN TRAN
IF @xtype = 'V'
SET @SQL = 'SELECT ' + @keys + ' FROM ' + @tablename + ' WITH (noexpand, INDEX (' + @indexname + '))' --
ELSE
SET @SQL = 'SELECT ' + @keys + ' FROM ' + @tablename + ' WITH (INDEX (' + @indexname + '))' --
EXEC(@SQL)
--ROLLBACK TRAN
FETCH NEXT FROM @cur INTO @indexname, @xtype, @keys
END
CLOSE @cur
DEALLOCATE @cur
END
GO
sys.dm_db_index_physical_stats
带有大多数参数为null
,并且最后一个参数为detailed
将读取所有页面。虽然不确定它是否会将所有内容保留在缓存中。有一些机制会不利于此,以避免淹没缓冲池。 - Martin Smith