减少连接查询的逻辑读取
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【中文标题】减少连接查询的逻辑读取【英文标题】:Reducing Logical Reads on Join Query 【发布时间】:2020-12-17 10:42:29 【问题描述】:希望有人可以帮助我。我们的客户有一个现有的数据库,这个特定的视图是有问题的并且运行速度非常慢。这是作为顾问向我们提出的,我到处都看到了带有聚集索引扫描的执行计划。我设法通过添加非聚集索引使其成为 Index Seek(除了少于 100 行的小表)
然而,我的问题是逻辑读取远非理想。这是查询计划的链接:https://www.brentozar.com/pastetheplan/?id=H1yKuqdnv
这是 IO 统计数据
SQL Server parse and compile time:
CPU time = 3906 ms, elapsed time = 4171 ms.
(5937 rows affected)
Table 'InsuranceVerificationType'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PatientInsuranceCIV'. Scan count 1, logical reads 4, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'VerificationStatusReason'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'VerificationStatus'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'VerificationStatusReasonStatus'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Language'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'OfficeAuth'. Scan count 5, logical reads 19, physical reads 1, read-ahead reads 13, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Attorney'. Scan count 5, logical reads 72, physical reads 0, read-ahead reads 80, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PatientAttorney'. Scan count 9, logical reads 870, physical reads 1, read-ahead reads 825, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'InsuranceType'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Carrier'. Scan count 5, logical reads 691, physical reads 1, read-ahead reads 230, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Team'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'WorkQueueItemStatus'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PriorityType'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PatientInsuranceRank'. Scan count 5, logical reads 11583, physical reads 1244, read-ahead reads 11484, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Office'. Scan count 5, logical reads 25, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'WorkQueueType'. Scan count 0, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PatientStatus'. Scan count 3, logical reads 6, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'TaxID'. Scan count 1, logical reads 2, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Workfile'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 11253, logical reads 43778, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'OfficeTaxID'. Scan count 5, logical reads 5102, physical reads 3, read-ahead reads 31, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'WorkQueueItem'. Scan count 5, logical reads 41408, physical reads 2, read-ahead reads 40993, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Patient'. Scan count 5, logical reads 23470, physical reads 0, read-ahead reads 22433, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Account'. Scan count 5, logical reads 13204, physical reads 1, read-ahead reads 12972, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Customer'. Scan count 0, logical reads 37098, physical reads 40, read-ahead reads 26760, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'CustomerAccount'. Scan count 7388, logical reads 75515, physical reads 47, read-ahead reads 20420, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PatientInsurance'. Scan count 5, logical reads 17379, physical reads 1, read-ahead reads 17158, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'ChargeHeaderFollowup'. Scan count 468, logical reads 3278, physical reads 1, read-ahead reads 3432, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PatientInsuranceVerificationHistory'. Scan count 5280, logical reads 42268, physical reads 3495, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
(1 row affected)
SQL Server Execution Times:
CPU time = 8185 ms, elapsed time = 80366 ms.
Completion time: 2020-12-17T16:15:59.3325424+08:00
使用 Patient 和 WorkQueueItem,我添加了这些索引
CREATE NONCLUSTERED INDEX [IX_WorkQueueItem_WorkQueueTypeID_ClosedDateUTC]
ON [dbo].[WorkQueueItem] ( [WorkQueueTypeId],[ClosedDateUtc] ) INCLUDE ( [WorkQueueItemId],[PriorityTypeId],[AssignedTo],[WorkQueueItemStatusId],[ItemKey], [CreatedDateUtc],[CreatedBy],[UpdatedDateUtc],[UpdatedBy],[TeamId],[PatientID], [PatientInsuranceID],[ChargeHeaderID] )
CREATE NONCLUSTERED INDEX [IX_Patient_Active_Deleted_PatientStatusID]
ON [dbo].[Patient] ( [Active],[Deleted], [PatientStatusID],[OfficeID])
INCLUDE ( [PatientID],[ThirdPartyPatientID],[InsuranceTypeID],[CarAccident],[AltIDStatusID])
这是完整的查询。
SELECT O.DeptNum as DeptNumber
,O.OfficeID
, O.AbbreviatedName AS LocationAbbreviatedName
, O.IsMSA
, A.PatientID
, P.ThirdPartyPatientID
, P.InsuranceTypeID AS PatientAccountType
, PIN.PatientInsuranceID
, A.ThirdPartyAccountID
, CU.Name AS FirstName
, CU.Name2 AS LastName
, CU.Name + ' ' + CU.Name2 AS PatientName
, IT.InsTypeDesc AS AccountType
, NULL AS RequestType
, PIR.Rank
, IsNull(C.Carrier, ATT.Firm) as Carrier
, P.CarAccident
, PIN.PolicyNumber
, Case
When P.InitialEvalDate Is Null Then
'01/01/1900'
Else
DATEADD(dd, DATEDIFF(dd, 0, P.InitialEvalDate), 0)
End InitialEvalDate
, Case
When P.InitialEvalDate Is Null Then
'01/01/1900 12:00 AM'
Else
P.InitialEvalDate
End AS InitialEvalDateTime
, PS.PatientStatusID
, PS.Status AS PatientStatus
, VS.VerificationStatusDescription AS CIVStatus
, VSR.VerificationStatusReasonDescription AS Reason
, L.LanguageDescription
, P.AltIDStatusID AS ReferralStatus
, T.TaxID
, T.TaxIDNickname
, wqi.WorkQueueItemId
, wqi.WorkQueueTypeId
, wqt.Name AS WorkQueueTypeName
, wqi.PriorityTypeId
, pt.Name AS PriorityTypeName
, wqi.WorkQueueItemStatusId
, wqis.WorkQueueItemStatusName
, wqi.AssignedTo
, wqi.ItemKey
, wqi.CreatedDateUtc
, wqi.CreatedBy
, wqi.UpdatedDateUtc
, wqi.UpdatedBy
, wqi.ClosedDateUtc
,Case
When wqi.ClosedDateUtc Is NULL Then
NULL
Else
DATEADD(dd, DATEDIFF(dd, 0, wqi.ClosedDateUtc), 0)
End ClosedDate
, wqi.TeamId
, tm.Name AS TeamName
, oa.TouchstoneLiveDate
,ivt.InsuranceVerificationTypeID
,ivt.[Description] AS InsuranceVerificationType
,chf.CalcDueDate AS DueDate
,IsNull(C.GenericCarrierCode, 0) as GenericCarrierCode
,C.ThirdPartyCarrierID
,wqi.ChargeHeaderID
FROM dbo.WorkQueueItem (NOLOCK) AS wqi
LEFT OUTER JOIN dbo.PatientInsurance (NOLOCK) AS PIN
ON PIN.PatientInsuranceID = wqi.PatientInsuranceID
INNER JOIN dbo.Patient (NOLOCK) AS P ON P.PatientID = wqi.PatientId AND P.Active = 1 AND P.Deleted = 0
INNER JOIN dbo.Account (NOLOCK) as A
ON A.PatientID = P.PatientID
INNER JOIN dbo.CustomerAccount (NOLOCK) AS CA ON CA.AccountID = A.AccountID AND CA.Deleted = 0
INNER JOIN dbo.Customer (NOLOCK) AS CU ON CU.CustomerID = CA.CustomerID AND CU.Deleted = 0
LEFT OUTER JOIN dbo.PatientInsuranceRank (NOLOCK) AS PIR ON PIR.PatientInsuranceID = PIN.PatientInsuranceID AND PIR.Deleted = 0
INNER JOIN dbo.WorkQueueType (NOLOCK) AS wqt ON wqt.WorkQueueTypeId = wqi.WorkQueueTypeId
LEFT OUTER JOIN dbo.PriorityType (NOLOCK) AS pt ON pt.PriorityTypeId = wqi.PriorityTypeId
LEFT OUTER JOIN dbo.WorkQueueItemStatus (NOLOCK) AS wqis ON wqis.WorkQueueItemStatusId = wqi.WorkQueueItemStatusId
LEFT OUTER JOIN dbo.Team (NOLOCK) AS tm ON tm.TeamId = wqi.TeamId
LEFT OUTER JOIN dbo.Carrier (NOLOCK) AS C ON C.CarrierID = PIN.CarrierID AND C.Deleted = 0
INNER JOIN dbo.Office (NOLOCK) AS O ON O.OfficeID = P.OfficeID AND O.Deleted = 0
LEFT OUTER JOIN dbo.InsuranceType (NOLOCK) AS IT ON IT.InsuranceTypeID = IsNull(C.InsuranceTypeID, P.InsuranceTypeID) AND IT.Deleted = 0
LEFT OUTER JOIN dbo.PatientAttorney (NOLOCK) as PATT on Patt.PatientID = P.PatientID AND PATT.AttorneyID <> 0 AND PATT.Deleted = 0
LEFT OUTER JOIN dbo.Attorney (NOLOCK) as ATT on ATT.AttorneyID = PATT.AttorneyID
INNER JOIN dbo.PatientStatus (NOLOCK) AS PS ON PS.PatientStatusID = P.PatientStatusID AND PS.PatientStatusID IN (1,2,4) AND PS.Deleted = 0
LEFT OUTER JOIN dbo.OfficeTaxID (NOLOCK) AS OT ON OT.OfficeID = O.OfficeID AND ((GETDATE() >= OT.EffectiveStartDate) AND ((GETDATE() <= OT.EffectiveEndDate) OR (OT.EffectiveEndDate IS NULL)))
LEFT OUTER JOIN OfficeAuth (NOLOCK) oa on p.OfficeID = oa.OfficeID
INNER JOIN dbo.TaxID (NOLOCK) AS T ON T.TaxIDID = OT.TaxIDID AND T.Deleted = 0
LEFT OUTER JOIN dbo.Language (NOLOCK) AS L ON L.LanguageID = CU.LanguageID AND L.Deleted = 0
LEFT OUTER JOIN PatientInsuranceVerificationHistory (NOLOCK) as phv
ON phv.PatientInsuranceVerificationHistoryID =
(
SELECT TOP 1 PatientInsuranceVerificationHistoryID
FROM PatientInsuranceVerificationHistory (NOLOCK)
WHERE PatientInsuranceVerificationHistory.PatientInsuranceID = PIN.PatientInsuranceID and deleted = 0
ORDER BY
PatientInsuranceVerificationHistory.CreatedDate DESC
)
LEFT OUTER JOIN dbo.VerificationStatusReasonStatus (NOLOCK) AS VSRS on phv.VerificationStatusReasonStatusID = VSRS.VerificationStatusReasonStatusID
LEFT OUTER JOIN dbo.VerificationStatus (NOLOCK) as VS on VSRS.VerificationStatusID = VS.VerificationStatusID
LEFT OUTER JOIN dbo.VerificationStatusReason (NOLOCK) as VSR on VSRS.VerificationStatusReasonID = VSR.VerificationStatusReasonID
LEFT OUTER JOIN dbo.PatientInsuranceCIV (NOLOCK) piciv ON piciv.PatientID = A.PatientID AND piciv.PatientInsuranceID = PIN.PatientInsuranceID
LEFT OUTER JOIN dbo.InsuranceVerificationType (NOLOCK) ivt ON ivt.InsuranceVerificationTypeID = piciv.VerificationTypeID
LEFT OUTER JOIN dbo.ChargeHeaderFollowup (NOLOCK) chf ON chf.ChargeHeaderID = wqi.ChargeHeaderID AND chf.Deleted = 0
WHERE wqi.WorkQueueTypeId = 2
AND ((PATT.EffectiveEndDate IS NULL) OR (GETDATE() >= PATT.EffectiveStartDate) AND (GETDATE() <= PATT.EffectiveEndDate))
AND ((wqi.ClosedDateUtc IS NULL) or (DATEDIFF(Day, wqi.ClosedDateUtc, GETUTCDATE()) < 30)
)
AND ISNULL(PIN.Deleted, 0) = 0
【问题讨论】:
上传实际执行计划。估计的计划估计有 600K 行。 最明显的问题是它返回了几千行,因为查询中没有真正的过滤器。有这么多行的应用程序在做什么?没有用户会读那么多。缺乏过滤器意味着扫描和哈希连接通常是要走的路,如果你想少读那么你会想要包含一些有意义的过滤器。如果这没有缺少过滤器,那么您可能希望以某种方式将这些循环更改为哈希连接(它们可能是由连接条件引起的)。使用nolock
意味着数据可能会以非常损坏的状态返回,这是故意的吗?
一些笔记。首先,视图通常设计为以这种方式使用:SELECT something, something FROM view WHERE some conditions
。如果您尝试在没有 WHERE 的情况下优化视图,则不会针对正确的查询进行优化,因为 WHERE 条件会选择索引。其次,SSMS 中的实际执行计划对索引提出建议。根据我的经验,这些建议通常非常有用。
查询没有过滤条件。这可能不适用于在线交易,但可能是报表查询或批量查询。您不应该期望任何这些都具有高性能,特别是如果您正在读取 100 万行。
看来计划只是缺少完整的SQL,请分享。此外,请确保这些索引提示实际上是有帮助的——它们以相当不受欢迎的方式被执行(即按索引顺序 1 比 1 读取表的每一行,而不是快速扫描表)
【参考方案1】:
很难知道从哪里开始,因为这是我无法访问的数据库上的一个巨大查询。但是从查询和查询计划中弹出给我的显而易见的事情如下:
NOLOCK
只有在您对返回的无效数据感到满意时才应使用。不仅是未提交的行,还有重复或计数不足的行。例如。如果您的状态或类型查找之一在您之下发生更改,您最终可能会加倍或删除具有这些 ID 的每一行。如果您遇到锁定问题,更好的选择是使用SNAPSHOT
隔离级别。
您真的需要返回所有这些列吗?减少每一次不必要的查找。您可以在客户端缓存状态和类型查找吗?
我没有您的架构,但如果任何左连接可以更改为内部连接,它可能会有所帮助,因为优化器可以更好地推理它们。此外,一些左连接依赖于先前的左连接,在这种情况下,嵌套连接可能更正确,并获得更好的结果。
在您查询Deleted = 0
的每个表上添加过滤索引,并将其用作过滤器。第一个索引列应该是适用表上的 StartDate。
PatientInsuranceVerificationHistory
上的联接应重写为 OUTER APPLY
。
根据基数,最好使用ROW_NUMBER()
过滤器加入整个PatientInsuranceVerificationHistory
。
OUTER APPLY
(
SELECT TOP 1 PatientInsuranceVerificationHistoryID
FROM PatientInsuranceVerificationHistory phv
WHERE phv.PatientInsuranceID = PIN.PatientInsuranceID and phv.deleted = 0
ORDER BY phv.CreatedDate DESC
) phv
PIN.Deleted
是否需要为空?如果没有,您可以按上述方法对其进行索引。
OfficeTaxID (OfficeID, StartDate)
上的索引会很有用。
针对OR
谓词的索引和基数估计总是很困难。一种可行的选择是手动编写索引联合,例如JOIN (SELECT * FROM a WHERE condition1 UNION ALL SELECT * FROM a WHERE condition2) a...
。
对于 EndDate(非常典型的 Type 2 SCD),提高效率的常见解决方案是:添加一个 IsCurrent 字段作为索引,或者将 EndDate 更改为使用 max-date (9999-12-31) 而不是 NULL (您可以将其作为计算列执行)。
倒数第二行可以改写如下: AND (wqi.ClosedDateUtc IS NULL OR wqi.ClosedDateUtc < DATEADD(Day, 30, GETUTCDATE())
这可能有助于基数估计并达到索引。DATEDIFF
对优化器来说很难推理,因为您要求它针对不等式运行代数:GETUTCDATE - ClosedDateUtc DATEADD你移动它说: ClosedDateUtc
【讨论】:
这几点很有用。我会尽力跟进并检查任何可能的变化。谢谢!完成后,我将更新此线程。真的很感激!以上是关于减少连接查询的逻辑读取的主要内容,如果未能解决你的问题,请参考以下文章
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