I’m trying to optimise a stored procedure and after looking at the execution plan and execution times I’m surprised by the results. Can anyone explain them.
The original SQL I wrote has 2 almost identical selects that I then pull together in a CTE, I tried to refactor that so the main work was done once, populating a table variable so I could then have 2 smaller selects that filtered the data the way I needed. The sole difference between the 2 select statements is the value that’s passed to TVF_GetChildGroups in the 1st select @AreaID represents the area of reporting for the current context and in the 2nd select @RootReportLevelID is simply all areas. So it’s the peers of the user context and the aim is to allow comparison between your scores and the average of everyone else.
DECLARE @Scores TABLE
(
ShortName VARCHAR(50) ,
PCTMax INT ,
PCTAvg INT ,
PCTMin INT ,
ALLAvg INT ,
AllMax INT ,
AllMin INT
)
INSERT INTO @Scores
SELECT T2.ShortName ,
MAX(T1.MeridianScore) AS PCTMax ,
CAST(( CAST(SUM(T1.contribution) AS DECIMAL) / CAST(SUM(T1.maxvalue) AS DECIMAL) * 100 ) AS DECIMAL(5, 2)) AS PCTAvg ,
MIN(T1.MeridianScore) AS PCTMin ,
CAST(( CAST(SUM(T2.contribution) AS DECIMAL) / CAST(SUM(T2.maxvalue) AS DECIMAL) * 100 ) AS DECIMAL(5, 2)) AS AllAvg ,
MAX(T2.MeridianScore) AS AllUpperScore ,
MIN(T2.MeridianScore) AS AllLowerScore
FROM ( SELECT US.PKID ,
PT.ShortName ,
CAST(( CAST(SUM(RES.contribution) AS DECIMAL) / CAST(SUM(RES.maxvalue) AS DECIMAL) * 100 ) AS DECIMAL(5, 2)) AS MeridianScore ,
SUM(Contribution) AS Contribution ,
SUM(MaxValue) AS MaxValue
FROM tblUploadedScorecards AS US
INNER JOIN tblUploadedScoreCardResults AS RES ON US.PKID = RES.FKUploadedScoreCardID
INNER JOIN tblUploadedScorecardHeaders AS USH ON USH.FKUploadedScorecardID = US.PKID
INNER JOIN @ProviderTable AS PT ON USH.HeaderValue = PT.FullName
INNER JOIN TVF_GetChildGroups(@AreaID) AS TGCG ON TGCG.GroupName = US.Branch
WHERE US.FKScoreCardID = 185
AND reviewed = 1
AND ShopDate BETWEEN @StartDate AND @EndDate
AND RES.Rating <> 'I'
AND USH.FKScorecardHeaderID = 71
GROUP BY US.PKID ,
PT.ShortName ) AS T1
RIGHT JOIN ( SELECT US.PKID ,
PT.ShortName ,
CAST(( CAST(SUM(RES.contribution) AS DECIMAL) / CAST(SUM(RES.maxvalue) AS DECIMAL) * 100 ) AS DECIMAL(5, 2)) AS MeridianScore ,
SUM(Contribution) AS Contribution ,
SUM(MaxValue) AS MaxValue
FROM tblUploadedScorecards AS US
INNER JOIN tblUploadedScoreCardResults AS RES ON US.PKID = RES.FKUploadedScoreCardID
INNER JOIN tblUploadedScorecardHeaders AS USH ON USH.FKUploadedScorecardID = US.PKID
INNER JOIN @ProviderTable AS PT ON USH.HeaderValue = PT.FullName
INNER JOIN TVF_GetChildGroups(@RootReportLevelID) AS TGCG ON TGCG.GroupName = US.Branch
WHERE US.FKScoreCardID = 185
AND reviewed = 1
AND ShopDate BETWEEN @StartDate AND @EndDate
AND RES.Rating <> 'I'
AND USH.FKScorecardHeaderID = 71
GROUP BY US.PKID ,
PT.ShortName ) AS T2 ON T1.ShortName = T2.ShortName
GROUP BY T2.ShortName
So I refactored out the commonality into a table variable against which I could apply the join to the TVF later in the hopes of not needing to hit the tables so much and ended up with this:
DECLARE @PreHierarchyResults TABLE
(
PKID INT ,
Branch VARCHAR(150) ,
ShortName VARCHAR(50) ,
Contribution DECIMAL(20,3),
MaxValue DECIMAL(20,3)
)
INSERT INTO @PreHierarchyResults
( PKID ,
Branch ,
ShortName ,
Contribution ,
MaxValue )
SELECT US.PKID ,
US.Branch ,
PT.ShortName ,
Contribution AS Contribution ,
MaxValue AS MaxValue
FROM tblUploadedScorecards AS US
INNER JOIN tblUploadedScoreCardResults AS RES ON US.PKID = RES.FKUploadedScoreCardID
INNER JOIN tblUploadedScorecardHeaders AS USH ON USH.FKUploadedScorecardID = US.PKID
INNER JOIN @ProviderTable AS PT ON USH.HeaderValue = PT.FullName
WHERE US.FKScoreCardID = 185
AND reviewed = 1
AND ShopDate BETWEEN @StartDate AND @EndDate
AND RES.Rating <> 'I'
AND USH.FKScorecardHeaderID = 71
INSERT INTO @Scores
SELECT T2.ShortName ,
MAX(T1.MeridianScore) AS PCTMax ,
CAST(( CAST(SUM(T1.contribution) AS DECIMAL) / CAST(SUM(T1.maxvalue) AS DECIMAL) * 100 ) AS DECIMAL(5, 2)) AS PCTAvg ,
MIN(T1.MeridianScore) AS PCTMin ,
CAST(( CAST(SUM(T2.contribution) AS DECIMAL) / CAST(SUM(T2.maxvalue) AS DECIMAL) * 100 ) AS DECIMAL(5, 2)) AS AllAvg ,
MAX(T2.MeridianScore) AS AllUpperScore ,
MIN(T2.MeridianScore) AS AllLowerScore
FROM ( SELECT PHR.PKID ,
ShortName ,
CAST(( CAST(SUM(contribution) AS DECIMAL) / CAST(SUM(maxvalue) AS DECIMAL) * 100 ) AS DECIMAL(5, 2)) AS MeridianScore ,
SUM(Contribution) AS Contribution ,
SUM(MaxValue) AS MaxValue
FROM @PreHierarchyResults AS PHR
INNER JOIN TVF_GetChildGroups(@AreaID) AS TGCG ON TGCG.GroupName = PHR.Branch
GROUP BY PHR.PKID , ShortName) AS T1
RIGHT JOIN ( SELECT PHR2.PKID ,
ShortName ,
CAST(( CAST(SUM(Contribution) AS DECIMAL) / CAST(SUM(Maxvalue) AS DECIMAL) * 100 ) AS DECIMAL(5, 2)) AS MeridianScore ,
SUM(Contribution) AS Contribution ,
SUM(MaxValue) AS MaxValue
FROM @PreHierarchyResults AS PHR2
INNER JOIN TVF_GetChildGroups(@RootReportLevelID) AS TGCG ON TGCG.GroupName = PHR2.Branch
GROUP BY PHR2.PKID , ShortName) AS T2 ON T1.ShortName = T2.ShortName
GROUP BY T2.ShortName
For the original SQL I get execution times:
SQL Server Execution Times:
CPU time = 16 ms, elapsed time = 11 ms.
Table ‘#012F94F2’. Scan count 0, logical reads 3, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘tblUploadedScoreCardResults’. Scan count 4456, logical reads 13943, physical reads 40, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘Worktable’. Scan count 6, logical reads 29800, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘tblUserGroups’. Scan count 2, logical reads 118, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘tblUploadedScorecards’. Scan count 0, logical reads 29496, physical reads 8, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘tblUploadedScorecardHeaders’. Scan count 192, logical reads 746, physical reads 5, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘#7D5F040E’. Scan count 186, logical reads 372, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
and after the refactoring I get:
SQL Server Execution Times:
CPU time = 0 ms, elapsed time = 10 ms.
Table ‘#48563EF2’. Scan count 0, logical reads 5106, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘tblUploadedScoreCardResults’. Scan count 185, logical reads 614, physical reads 41, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘tblUploadedScorecards’. Scan count 0, logical reads 370, physical reads 8, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘tblUploadedScorecardHeaders’. Scan count 7, logical reads 23, physical reads 5, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘#439189D5’. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
(5059 row(s) affected)
(1 row(s) affected)SQL Server Execution Times:
CPU time = 16 ms, elapsed time = 199 ms.
Table ‘#47621AB9’. Scan count 0, logical reads 3, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘Worktable’. Scan count 114, logical reads 1770, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘tblUserGroups’. Scan count 112, logical reads 998, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table ‘#48563EF2’. Scan count 112, logical reads 5376, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Looking at the output I think it’s clear that the first version is more efficient, but I just don’t understand why it should be the case as it appears to hit 4 tables twice whereas in the 2nd version those tables are only hit the one time.
I would also compare the actual execution plans between your original and revised queries.
Also check the indexes on
tblUploadedScorecards,tblUploadedScoreCardResults, andtblUploadedScorecardHeaders. After caching data from those tables into @PreHierarchyResults, you might be losing the benefits of some covering indexes on the join columns in your second query.