服务器重启后首次运行大表查询需要很长时间

Posted 2023-04-18

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【中文标题】服务器重启后首次运行大表查询需要很长时间【英文标题】：First run of query on big table takes very long after server restart 【发布时间】：2016-07-21 10:21:32 【问题描述】：

在服务器重新启动后，当我运行以下查询时，它需要很长时间。该表有 1.500.000 行，查询返回 140.000 行。

select 
Oid, -- Primary Key 
IsTranslated -- bool(bit) column
from Translation
where [Language] = '24648b4e-05ac-42cb-b6cf-c1167b6a41b7'

语言列上有一个索引。服务器重启后的第一次运行需要 6 分钟才能完成，后续查询需要 1-2 秒才能完成。将“WITH(INDEX(iLanguage_Translation))”添加到查询的 FROM 部分并没有提高性能。

但是在服务器重启后的第一次运行中，follownig 查询只需 2 秒即可完成：

select Oid -- Primary Key
from Translation
where [Language] = '24648b4e-05ac-42cb-b6cf-c1167b6a41b7'

这两个查询之间的唯一区别是一个额外的 bool(bit) 列。为什么传输 140.000 行的额外位列需要 6 分钟？

我有带有 i7 2700K 处理器和 16GB 内存的 SQL Server 2014。

这是表创建脚本：

CREATE TABLE [dbo].[Translation](
    [Oid] [uniqueidentifier] ROWGUIDCOL  NOT NULL,
    [PropertyName] [nvarchar](max) NULL,
    [DefaultLanguageValue] [nvarchar](max) NULL,
    [TranslatedValue] [nvarchar](max) NULL,
    [IsTranslated] [bit] NULL,
    [NodePath] [nvarchar](max) NULL,
    [Description] [nvarchar](max) NULL,
    [Language] [uniqueidentifier] NULL,
    [OptimisticLockField] [int] NULL,
    [GCRecord] [int] NULL,
 CONSTRAINT [PK_Translation] PRIMARY KEY CLUSTERED 
(
    [Oid] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

GO

/****** Object:  Index [iGCRecord_Translation]    Script Date: 2016.07.21. 12:09:08 ******/
CREATE NONCLUSTERED INDEX [iGCRecord_Translation] ON [dbo].[Translation]
(
    [GCRecord] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO

/****** Object:  Index [iLanguage_Translation]    Script Date: 2016.07.21. 12:09:08 ******/
CREATE NONCLUSTERED INDEX [iLanguage_Translation] ON [dbo].[Translation]
(
    [Language] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO

ALTER TABLE [dbo].[Translation]  WITH NOCHECK ADD  CONSTRAINT [FK_Translation_Language] FOREIGN KEY([Language])
REFERENCES [dbo].[Language] ([Oid])
NOT FOR REPLICATION 
GO

ALTER TABLE [dbo].[Translation] CHECK CONSTRAINT [FK_Translation_Language]
GO

将在我的网络应用程序中使用的最终查询使用表的所有列：

SELECT [Oid]
      ,[PropertyName]
      ,[DefaultLanguageValue]
      ,[TranslatedValue]
      ,[IsTranslated]
      ,[NodePath]
      ,[Description]
      ,[Language]
      ,[OptimisticLockField]
      ,[GCRecord]
  FROM [dbo].[Translation]
  where [Language] = '24648b4e-05ac-42cb-b6cf-c1167b6a41b7'

执行计划：

执行计划 XML：

<?xml version="1.0" encoding="utf-16"?>
<ShowPlanXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Version="1.2" Build="12.0.4459.0" xmlns="http://schemas.microsoft.com/sqlserver/2004/07/showplan">
  <BatchSequence>
    <Batch>
      <Statements>
        <StmtSimple StatementCompId="1" StatementEstRows="171288" StatementId="1" StatementOptmLevel="FULL" CardinalityEstimationModelVersion="120" StatementSubTreeCost="102.045" StatementText="SELECT [Oid],[PropertyName],[DefaultLanguageValue],[TranslatedValue],[IsTranslated],[NodePath],[Description],[Language],[OptimisticLockField],[GCRecord] FROM [dbo].[Translation] WHERE [Language]=@1" StatementType="SELECT" QueryHash="0x7722D3C37A4ACDF4" QueryPlanHash="0xEBAED5C218B1FD8D" RetrievedFromCache="false">
          <StatementSetOptions ANSI_NULLS="true" ANSI_PADDING="true" ANSI_WARNINGS="true" ARITHABORT="true" CONCAT_NULL_YIELDS_NULL="true" NUMERIC_ROUNDABORT="false" QUOTED_IDENTIFIER="true" />
          <QueryPlan DegreeOfParallelism="1" CachedPlanSize="24" CompileTime="475" CompileCPU="2" CompileMemory="184">
            <MemoryGrantInfo SerialRequiredMemory="0" SerialDesiredMemory="0" />
            <OptimizerHardwareDependentProperties EstimatedAvailableMemoryGrant="209425" EstimatedPagesCached="104712" EstimatedAvailableDegreeOfParallelism="4" />
            <RelOp AvgRowSize="20181" EstimateCPU="2.07874" EstimateIO="99.9661" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="171288" LogicalOp="Clustered Index Scan" NodeId="0" Parallel="false" PhysicalOp="Clustered Index Scan" EstimatedTotalSubtreeCost="102.045" TableCardinality="1889620">
              <OutputList>
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="Oid" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="PropertyName" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="DefaultLanguageValue" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="TranslatedValue" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="IsTranslated" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="NodePath" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="Description" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="Language" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="OptimisticLockField" />
                <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="GCRecord" />
              </OutputList>
              <RunTimeInformation>
                <RunTimeCountersPerThread Thread="0" ActualRows="144003" ActualEndOfScans="1" ActualExecutions="1" />
              </RunTimeInformation>
              <IndexScan Ordered="false" ForcedIndex="false" ForceScan="false" NoExpandHint="false" Storage="RowStore">
                <DefinedValues>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="Oid" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="PropertyName" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="DefaultLanguageValue" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="TranslatedValue" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="IsTranslated" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="NodePath" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="Description" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="Language" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="OptimisticLockField" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="GCRecord" />
                  </DefinedValue>
                </DefinedValues>
                <Object Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Index="[PK_Translation]" IndexKind="Clustered" Storage="RowStore" />
                <Predicate>
                  <ScalarOperator ScalarString="[vintocon.archifm.Loc].[dbo].[Translation].[Language]=guid'24648B4E-05AC-42CB-B6CF-C1167B6A41B7'">
                    <Compare CompareOp="EQ">
                      <ScalarOperator>
                        <Identifier>
                          <ColumnReference Database="[vintocon.archifm.Loc]" Schema="[dbo]" Table="[Translation]" Column="Language" />
                        </Identifier>
                      </ScalarOperator>
                      <ScalarOperator>
                        <Const ConstValue="guid'24648B4E-05AC-42CB-B6CF-C1167B6A41B7'" />
                      </ScalarOperator>
                    </Compare>
                  </ScalarOperator>
                </Predicate>
              </IndexScan>
            </RelOp>
            <ParameterList>
              <ColumnReference Column="@1" ParameterCompiledValue="'24648b4e-05ac-42cb-b6cf-c1167b6a41b7'" ParameterRuntimeValue="'24648b4e-05ac-42cb-b6cf-c1167b6a41b7'" />
            </ParameterList>
          </QueryPlan>
        </StmtSimple>
      </Statements>
    </Batch>
  </BatchSequence>
</ShowPlanXML>

【问题讨论】：

我想是关于缓存的。尝试DBCC DROPCLEANBUFFERS 而不是重新启动 - 应该有相同的效果。我也猜想这是第一次使用页面时缓冲池填满。鉴于您在聚集键是 GUID 的聚集索引中保存了 150 万行，我猜该索引非常分散，这可以解释为什么将所有页面读入内存需要很长时间。 【参考方案1】：

阅读KeyLookup关于执行计划的操作并创建一个覆盖索引：

CREATE NONCLUSTERED INDEX [iLanguage_Translation]
    ON [dbo].[Translation] ([Language]) INCLUDE (IsTranslated)

【讨论】：

问题是在我的最终查询中我需要select中的所有列，而varchar(max)列不能用作索引在您的问题中，我看不到任何最终查询...请更新您的问题并提供实际执行计划更新问题

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