Read/interpret XML query estimation plan to get estimate rows count
Question
I'm trying to programtically get the estimated rows for a query in c#.NET
I'm setting
"SET SHOWPLAN_XML ON;";
before running a query, to get the estimation plan.
The thing returned for a simple select on one table contains a lot of data and I see that EstimateRows attribute is present 3 times in the XML.
For a query which JOIN s multiple tables The EstimateRows is present even more times.
Example:
<?xml version="1.0" encoding="UTF-8"?>
<ShowPlanXML xmlns="http://schemas.microsoft.com/sqlserver/2004/07/showplan" Version="1.5" Build="14.0.100.430">
<BatchSequence>
<Batch>
<Statements>
<StmtSimple StatementText="SELECT COUNT(DISTINCT co.Id) FROM Campaign &#xd;&#xa;as ca JOIN KPI_EmailOpened as eo ON eo.CampaignId = ca.Id JOIN Contact&#xd;&#xa; AS co ON co.Id = eo.ContactId &#xd;&#xa;WHERE co.FirstName = &apos;John&apos;" StatementId="1" StatementCompId="1" StatementType="SELECT" RetrievedFromCache="false" StatementSubTreeCost="2.98809" StatementEstRows="1" SecurityPolicyApplied="false" StatementOptmLevel="FULL" QueryHash="0x5E01ED198558D453" QueryPlanHash="0xBD8133A97EEAAC2C" CardinalityEstimationModelVersion="130">
<StatementSetOptions QUOTED_IDENTIFIER="true" ARITHABORT="true" CONCAT_NULL_YIELDS_NULL="true" ANSI_NULLS="true" ANSI_PADDING="true" ANSI_WARNINGS="true" NUMERIC_ROUNDABORT="false" />
<QueryPlan NonParallelPlanReason="EstimatedDOPIsOne" CachedPlanSize="48" CompileTime="9" CompileCPU="9" CompileMemory="816">
<MemoryGrantInfo SerialRequiredMemory="3072" SerialDesiredMemory="3104" />
<OptimizerHardwareDependentProperties EstimatedAvailableMemoryGrant="17616030" EstimatedPagesCached="1101001" EstimatedAvailableDegreeOfParallelism="1" MaxCompileMemory="4603408" />
<RelOp NodeId="1" PhysicalOp="Compute Scalar" LogicalOp="Compute Scalar" EstimateRows="1" EstimateIO="0" EstimateCPU="1e-007" AvgRowSize="11" EstimatedTotalSubtreeCost="2.98809" Parallel="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row">
<OutputList>
<ColumnReference Column="Expr1003" />
</OutputList>
<ComputeScalar>
<DefinedValues>
<DefinedValue>
<ColumnReference Column="Expr1003" />
<ScalarOperator ScalarString="CONVERT_IMPLICIT(int,[globalagg1005],0)">
<Convert DataType="int" Style="0" Implicit="1">
<ScalarOperator>
<Identifier>
<ColumnReference Column="globalagg1005" />
</Identifier>
</ScalarOperator>
</Convert>
</ScalarOperator>
</DefinedValue>
</DefinedValues>
<RelOp NodeId="2" PhysicalOp="Stream Aggregate" LogicalOp="Aggregate" EstimateRows="1" EstimateIO="0" EstimateCPU="1.1e-006" AvgRowSize="15" EstimatedTotalSubtreeCost="2.98809" Parallel="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row">
<OutputList>
<ColumnReference Column="globalagg1005" />
</OutputList>
<StreamAggregate>
<DefinedValues>
<DefinedValue>
<ColumnReference Column="globalagg1005" />
<ScalarOperator ScalarString="SUM([partialagg1004])">
<Aggregate Distinct="0" AggType="SUM">
<ScalarOperator>
<Identifier>
<ColumnReference Column="partialagg1004" />
</Identifier>
</ScalarOperator>
</Aggregate>
</ScalarOperator>
</DefinedValue>
</DefinedValues>
<RelOp NodeId="3" PhysicalOp="Hash Match" LogicalOp="Aggregate" EstimateRows="1" EstimateIO="0" EstimateCPU="0.00188442" AvgRowSize="15" EstimatedTotalSubtreeCost="2.98809" Parallel="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Batch">
<OutputList>
<ColumnReference Column="partialagg1004" />
</OutputList>
<MemoryFractions Input="1" Output="1" />
<Hash>
<DefinedValues>
<DefinedValue>
<ColumnReference Column="partialagg1004" />
<ScalarOperator ScalarString="COUNT(*)">
<Aggregate Distinct="0" AggType="COUNT*" />
</ScalarOperator>
</DefinedValue>
</DefinedValues>
<HashKeysBuild />
<RelOp NodeId="5" PhysicalOp="Nested Loops" LogicalOp="Left Semi Join" EstimateRows="10934.3" EstimateIO="0" EstimateCPU="0.0457056" AvgRowSize="9" EstimatedTotalSubtreeCost="2.98609" Parallel="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row">
<OutputList />
<NestedLoops Optimized="0" WithUnorderedPrefetch="1">
<OuterReferences>
<ColumnReference Database="[mydb]" Schema="[dbo]" Table="[Contact]" Alias="[co]" Column="Id" />
<ColumnReference Column="Expr1013" />
</OuterReferences>
<RelOp NodeId="7" PhysicalOp="Index Seek" LogicalOp="Index Seek" EstimateRows="10934.4" EstimatedRowsRead="10934.4" EstimateIO="0.0601111" EstimateCPU="0.0121848" AvgRowSize="19" EstimatedTotalSubtreeCost="0.0722959" TableCardinality="1e+007" Parallel="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row">
<OutputList>
<ColumnReference Database="[mydb]" Schema="[dbo]" Table="[Contact]" Alias="[co]" Column="Id" />
</OutputList>
<IndexScan Ordered="1" ScanDirection="FORWARD" ForcedIndex="0" ForceSeek="0" ForceScan="0" NoExpandHint="0" Storage="RowStore">
<DefinedValues>
<DefinedValue>
<ColumnReference Database="[mydb]" Schema="[dbo]" Table="[Contact]" Alias="[co]" Column="Id" />
</DefinedValue>
</DefinedValues>
<Object Database="[mydb]" Schema="[dbo]" Table="[Contact]" Index="[IX_Contact_FirstName]" Alias="[co]" IndexKind="NonClustered" Storage="RowStore" />
<SeekPredicates>
<SeekPredicateNew>
<SeekKeys>
<Prefix ScanType="EQ">
<RangeColumns>
<ColumnReference Database="[mydb]" Schema="[dbo]" Table="[Contact]" Alias="[co]" Column="FirstName" />
</RangeColumns>
<RangeExpressions>
<ScalarOperator ScalarString="&apos;John&apos;">
<Const ConstValue="&apos;John&apos;" />
</ScalarOperator>
</RangeExpressions>
</Prefix>
</SeekKeys>
</SeekPredicateNew>
</SeekPredicates>
</IndexScan>
</RelOp>
<RelOp NodeId="8" PhysicalOp="Index Seek" LogicalOp="Index Seek" EstimateRows="1" EstimatedRowsRead="30.0011" EstimateIO="0.003125" EstimateCPU="0.000190001" AvgRowSize="9" EstimatedTotalSubtreeCost="2.86809" TableCardinality="2.95e+008" Parallel="0" EstimateRebinds="10933.4" EstimateRewinds="0" EstimatedExecutionMode="Row">
<OutputList />
<IndexScan Ordered="1" ScanDirection="FORWARD" ForcedIndex="0" ForceSeek="0" ForceScan="0" NoExpandHint="0" Storage="RowStore">
<DefinedValues />
<Object Database="[mydb]" Schema="[dbo]" Table="[KPI_EmailOpened]" Index="[KPI_EmailOpened_NCIDX_ContactCampaign]" Alias="[eo]" IndexKind="NonClustered" Storage="RowStore" />
<SeekPredicates>
<SeekPredicateNew>
<SeekKeys>
<Prefix ScanType="EQ">
<RangeColumns>
<ColumnReference Database="[mydb]" Schema="[dbo]" Table="[KPI_EmailOpened]" Alias="[eo]" Column="ContactId" />
</RangeColumns>
<RangeExpressions>
<ScalarOperator ScalarString="[mydb].[dbo].[Contact].[Id] as [co].[Id]">
<Identifier>
<ColumnReference Database="[mydb]" Schema="[dbo]" Table="[Contact]" Alias="[co]" Column="Id" />
</Identifier>
</ScalarOperator>
</RangeExpressions>
</Prefix>
</SeekKeys>
</SeekPredicateNew>
</SeekPredicates>
</IndexScan>
</RelOp>
</NestedLoops>
</RelOp>
</Hash>
</RelOp>
</StreamAggregate>
</RelOp>
</ComputeScalar>
</RelOp>
</QueryPlan>
</StmtSimple>
</Statements>
</Batch>
most of them show 1 as estimation, except two which are very close to the actual result:(around 10500 rows)
<RelOp NodeId="5" PhysicalOp="Nested Loops" LogicalOp="Left Semi Join" EstimateRows="10934.3" EstimateIO="0" EstimateCPU="0.0457056" AvgRowSize="9" EstimatedTotalSubtreeCost="2.98609" Parallel="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row">
and
<RelOp NodeId="7" PhysicalOp="Index Seek" LogicalOp="Index Seek" EstimateRows="10934.4" EstimatedRowsRead="10934.4" EstimateIO="0.0601111" EstimateCPU="0.0121848" AvgRowSize="19" EstimatedTotalSubtreeCost="0.0722959" TableCardinality="1e+007" Parallel="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row">
I'm trying to find articles on how to read these values but couldn't find much.
Can you tell or point me to some articles which explain how to read this XML and how to get the estimated row count for any query?
1 answers
solution1
0 2019-11-05 19:40:41
As you do a count I think the 1 is the correct one for returning the number of records. This is also node 1 which is the aggregate/last step of the execution plan (you read them frm right to left). The other nodes are intermediate nodes with intermediate results (like the 10500) that are the basis for the count.
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