我在 SQL Server 中有一个如下所示的表:
CREATE TABLE [dbo].[FCT_RawEvents](
[EquipID] [int] NOT NULL,
[EventTimeStamp] [int] NOT NULL,
[EventMilliSeconds] [smallint] NULL,
[EventID] [int] NOT NULL,
[EventOn] [bit] NOT NULL,
[JobID] [int] NULL,
[FirstEvent] [bit] NULL,
[OperatorId] [int] NULL,
[Suppressed] [bit] NULL,
[ManualOverride] [bit] NULL
)
这包含打开或关闭的事件(EventOn = True,EventOn = False)。现在我需要在给定时间获取所有“事件”(未抑制)的事件。我有一些可用的 SQL,但是由于此表有数百万行,它运行起来非常慢(5 个 equipIds 需要 10 秒)。
这里是:
DECLARE @StartDateTime datetime = '2013/01/01'
DECLARE @csvEquipIds nvarchar(MAX) = '5,6,7,8'
DECLARE @StartTimeStamp int = dbo.GetSecondsFromDate(@StartDateTime)
DECLARE @StartMilliSeconds smallint = DATEPART(Ms, @StartDateTime)
DECLARE @EquipIds TABLE (EquipId int)
INSERT INTO @EquipIds(EquipId) SELECT EquipID FROM dbo.getEquipmentIDs(null,@csvEquipIds)
SELECT dbo.getDateFromSeconds(EventTimeStamp), * FROM
( SELECT re.EquipID,EventTimeStamp,EventMilliSeconds,EventID,eventon,
ROW_NUMBER() OVER (PARTITION BY re.EquipId,EventID ORDER BY EventTimeStamp DESC,EventMilliSeconds DESC) AS RowNo
FROM dbo.FCT_RawEvents re
JOIN @EquipIds eq
ON eq.EquipId = re.EquipID
WHERE (re.EventTimeStamp < @StartTimeStamp OR(re.EventTimeStamp = @StartTimeStamp AND re.EventMilliSeconds <= @StartMilliSeconds)) AND re.EventID > 0
AND (re.Suppressed IS NULL)-- OR re.Suppressed = 0)
) ev
WHERE RowNo = 1 AND EventOn = 1
ORDER BY EquipID,EventID, EventTimeStamp desc, EventMilliSeconds desc
执行计划表明80%的时间花在了排序上,也就是Partition/Order窗口函数。
我绝不是 INDEX 专家,但添加了这些:
CREATE CLUSTERED INDEX [IX_Clustered] ON [dbo].[FCT_RawEvents]
(
[EquipID] ASC,
[EventTimeStamp] DESC,
[EventMilliSeconds] DESC,
[EventID] ASC,
[EventOn] DESC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
CREATE NONCLUSTERED INDEX [IX_EquipEventTime] ON [dbo].[FCT_RawEvents]
(
[EquipID] ASC,
[EventID] ASC,
[EventTimeStamp] DESC,
[EventMilliSeconds] DESC
)
INCLUDE ( [EventOn]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
CREATE NONCLUSTERED INDEX [IX_Suppressed] ON [dbo].[FCT_RawEvents]
(
[Suppressed] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
看起来排序正在扫描表的很大一部分,我真的希望它在找到第一个匹配事件之前“回头看”。
任何指针都将不胜感激,无论是通过使用索引还是改进 SQL。
最佳答案
跟进评论:
尝试用临时表替换表变量:表变量没有统计信息,临时表可以。
第二个索引看起来是多余的。
尝试替换标量值函数。
检查色谱柱的选择性
EquipID, EventTimeStamp, EventMilliSeconds, EventID, EventOn
并按照选择性从高到低的顺序创建索引。选择性是衡量一列中有多少重复值的指标。它的范围从无重复(高选择性)到所有相同的值(零选择性)。理想情况下,索引应按最高选择性顺序排列列。
例如,EquipId
列的选择性将是
(SELECT COUNT(DISTINCT EquipId) FROM dbo.FCT_RawEvents) /
(SELECT COUNT(*) FROM dbo.FCT_RawEvents)
- 确保您的统计数据是最新的。
关于SQL Server 索引/SQL 性能增强,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/14477536/