即使我有很好的索引
无意冒犯,但让我们来判断一下。始终发布exact当询问 SQL Server 性能问题时,表的架构,包括所有索引和基数。
例如,让我们考虑以下表结构:
create table tblSequence (
[UserSessionSequenceID] int not null
,[SessionGuid] uniqueidentifier not null
,[SiteID] int not null
,[Timestamp] datetime not null
, filler varchar(512));
go
create clustered index cdxSequence on tblSequence (SiteID, [Timestamp]);
go
与您的相同,但与性能问题无关的所有字段都聚合到通用填充符中。让我们看看,例如,大约 50k 会话的 1M 行的性能有多差?让我们用随机数据填充表格,但我们将模拟“用户活动”的内容:
set nocount on;
declare @i int = 0, @sc int = 1;
declare @SessionGuid uniqueidentifier = newid()
, @siteID int = 1
, @Timestamp datetime = dateadd(day, rand()*1000, '20070101')
, @UserSessionSequenceID int = 0;
begin tran;
while @i<1000000
begin
insert into tblSequence (
[UserSessionSequenceID]
,[SessionGuid]
,[SiteID]
,[Timestamp]
, filler)
values (
@UserSessionSequenceID
, @SessionGuid
, @siteID
, @timestamp
, replicate('X', rand()*512));
if rand()*100 < 5
begin
set @SessionGuid = newid();
set @siteID = rand() * 10;
set @Timestamp = dateadd(day, rand()*1000, '20070101');
set @UserSessionSequenceID = 0;
set @sc += 1;
end
else
begin
set @timestamp = dateadd(second, rand()*300, @timestamp);
set @UserSessionSequenceID += 1;
end
set @i += 1;
if (@i % 1000) = 0
begin
raiserror(N'Inserted %i rows, %i sessions', 0, 1, @i, @sc);
commit;
begin tran;
end
end
commit;
这大约需要 1 分钟才能充满。现在让我们查询您提出的相同查询:过去 Y 分钟内站点 X 上的任何用户会话的最后一个操作是什么?我必须使用@now的特定日期而不是GETDATE(),因为emy dtaa是模拟的,而不是真实的,所以我使用为SiteId 1随机填充的最大时间戳:
set statistics time on;
set statistics io on;
declare @resultCount int = 30;
declare @minutes int = 60*24;
declare @siteID int = 1;
declare @now datetime = '2009-09-26 02:08:27.000';
SELECT TOP(@resultCount) * FROM
(
SELECT
[UserSessionSequenceID]
,[SessionGuid]
, SiteID
, Filler
,[Timestamp]
,ROW_NUMBER() over (PARTITION BY [SessionGuid]
ORDER BY UserSessionSequenceID DESC) AS sort
FROM [tblSequence]
where SiteID = @siteID
and [Timestamp] > DATEADD(mi, -@minutes, @now)
) AS t
WHERE sort = 1
ORDER BY [UserSessionSequenceID] DESC ;
这与您的查询相同,但限制性过滤器已移动insideROW_NUMBER() 部分子查询。结果返回:
Table 'tblSequence'. Scan count 1, logical reads 12, physical reads 0.
SQL Server Execution Times:
CPU time = 0 ms, elapsed time = 31 ms.
热缓存上的响应时间为 31 毫秒,从表的近 60k 页中读取了 12 页。
Updated
再次阅读原始查询后,我意识到修改后的查询是不同的。你只需要new会议。我仍然相信通过 SiteID 和 Timestmap 进行过滤是获得必要性能的唯一方法,因此解决方案是使用 NOT EXISTS 条件验证候选发现:
SELECT TOP(@resultCount) * FROM
(
SELECT
[UserSessionSequenceID]
,[SessionGuid]
, SiteID
, Filler
,[Timestamp]
,ROW_NUMBER() over (
PARTITION BY [SessionGuid]
ORDER BY UserSessionSequenceID DESC)
AS sort
FROM [tblSequence]
where SiteID = @siteID
and [Timestamp] > DATEADD(mi, -@minutes, @now)
) AS new
WHERE sort = 1
and not exists (
select SessionGuid
from tblSequence
where SiteID = @siteID
and SessionGuid = new.SessionGuid
and [TimeStamp] < DATEADD(mi, -@minutes, @now)
)
ORDER BY [UserSessionSequenceID] DESC
这在我的笔记本电脑上返回,在 40 毫秒内从热缓存中返回超过 400k 会话的 1M 行:
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0
Table 'tblSequence'. Scan count 2, logical reads 709, physical reads 0
SQL Server Execution Times:
CPU time = 16 ms, elapsed time = 40 ms.