Jul 23, 2005
Hi,My company has a scenario where we would like to change the data typeof an existing primary key from an integer to a char, but we areconcerned about the performance implications of doing so. The scriptfor the two tables that we need to modify is listed below. TableFR_Sessions contains a column named TransmissionID which is currentlyan integer. This table contains about 1 million rows of data. TableFR_VTracking table also contains the TransmissionID as part of it'sprimary key and it contains about 35 millions rows of data. These twotables are frequently joined on TransmissionID (FR_Sessions is theparent). The TransmissionID column is used primarily for joins and isnot typically displayed.We need like to change the TransmissionID data type from int tochar(7), and I had a few questions:1) Would this introduce significant performance degradation? I haveread that char keys/indexes are slower than int/numeric.2) Are there collation options (or any other optimizations) that wecould use to minimize the performance hit of the char(7)...if so whichones?I am a software architect by trade, not a database guru, so please goeasy on my if I overlooked something obvious :)Any suggestions or information would be greatly appreciated.Thanks,Tim-------------------CREATE TABLE [FR_Sessions] ([TransmissionID] [int] IDENTITY (1, 1) NOT NULL ,[PTUID] [varchar] (10) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,[PortNum] [numeric](6, 0) NOT NULL CONSTRAINT [DF_FR_Sessions_PortNum]DEFAULT (0),[CloseStatus] [varchar] (20) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,[RecvBytes] [int] NULL ,[SendBytes] [int] NULL ,[EndDT] [datetime] NULL CONSTRAINT [DF_FR_Sessions_EndDT] DEFAULT(getutcdate()),[LocalEndDT] [datetime] NULL ,[TotalTime] [int] NULL ,[OffenderID] [numeric](9, 0) NULL ,[UploadStatus] [char] (1) COLLATE SQL_Latin1_General_CP1_CI_AS NOTNULL CONSTRAINT [DF_FR_Sessions_UploadStatus] DEFAULT ('N'),[SchedBatchID] [numeric](18, 0) NULL ,[SWVersion] [varchar] (10) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,[DLST] [bit] NULL ,[TZO] [smallint] NULL ,[Processed] [bit] NOT NULL CONSTRAINT [DF_FR_Sessions_Processed]DEFAULT (0),[CallerID] [varchar] (13) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,[PeerIP] [varchar] (16) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,[XtraInfo] [varchar] (1024) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,[IdType] [char] (1) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,CONSTRAINT [PK_FR_Sessions] PRIMARY KEY CLUSTERED([TransmissionID]) WITH FILLFACTOR = 90 ON [PRIMARY]) ON [PRIMARY]CREATE TABLE [FR_VTracking] ([TransmissionID] [int] NOT NULL ,[FrameNum] [int] NOT NULL ,[LatDegrees] [float] NOT NULL ,[LonDegrees] [float] NOT NULL ,[Altitude] [float] NOT NULL ,[Velocity] [float] NOT NULL ,[NumPositions] [smallint] NOT NULL ,[NavMode] [smallint] NOT NULL ,[Units] [smallint] NOT NULL ,[GPSTrackingID] [numeric](18, 0) IDENTITY (1, 1) NOT NULL ,[dtStamp] [datetime] NULL ,CONSTRAINT [PK_FR_VTracking] PRIMARY KEY CLUSTERED([TransmissionID],[FrameNum]) WITH FILLFACTOR = 90 ON [PRIMARY]) ON [PRIMARY]
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May 15, 2008
I was hoping I wouldn't be another poster with performance issues after migrating to SQl 2005 from SQL 2000 but here I am.
I am in the process of testing out our databases on Sql Server 2005 for migration from SQL Server 2000 and there are certain portions of code that have been affected negatively. I have read thru many of the posts here and have tried out most of the recommendations. I will start out with things I've done and then provide the actual SQL.
1) I have rebuilt all indexes ( using the DBCC REINDEX using the table option).
2) Updated the db engine to latest hot fix (build 3239) that addresses speed related fixes.
3) I also ran sp_createstats using the 'fullscan' option to create stats on all columns of all tables (minus indexed columns)
4) Since nothing seemed to work, I even ran UPDATE STATICS with FULL SCAN on all tables even though I did not need it as the REBUILD woudl have created stats. But I was willing to try anything.
I have confirmed that the execution plans are different even though the data on both sql 2000 and sql 2005 are identical (i put a copy on 2005). The plans themselves are huge as the queries are huge. Here is the query.
SELECT InterimView.* ,TestView.*
FROM View_LabDataExport_TestFormData_55 TestView
RIGHT OUTER JOIN ( SELECT ReqView.*, CDView.*
FROM View_LabDataExport_FormData_55 ReqView
LEFT OUTER JOIN View_LabDataExport_FormData_CD_55 CDView
ON ( CDView.DB_SubjectID_CD = ReqView.DB_SUbjectID )
) InterimView
ON ( InterimView.DB_FormID = TestView.DB_FormID_T AND
InterimView.DB_LabSampleID = TestView.DB_LabSampleID_T )
The above query takes abotu 8 secs to run on 2000 and about 1 minute to run on 2005. This is for a small dataset and on larger datasets this is only going to more pronounced ( as confirmed by other teams that have already migrated in my company). Another point worth mentioning might be if I remove the TestView.* from the select list, it works in 5 to 6 seconds. Is there an issue with Sql 2005 and a large number of columns or anything of that sort? On 2000, the time remains the same , about 8 seconds if I remove this from the select list.
Here is the statistics ion on 2005
(21234 row(s) affected)
Table 'Worktable'. Scan count 75490, logical reads 3676867, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LabTestToReportPanel'. Scan count 476, logical reads 1524, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LabReportPanel'. Scan count 0, logical reads 260, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'DiscreteValue'. Scan count 1, logical reads 176106, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LabReleasedSampleTest'. Scan count 1, logical reads 2078, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LabSample'. Scan count 1360, logical reads 18567, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Form'. Scan count 2302, logical reads 8225, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LabTest'. Scan count 1, logical reads 23, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LabSampleDef'. Scan count 1, logical reads 10530, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LabArea'. 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.
Table 'Lab'. 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.
Table 'Location'. 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.
Table 'Study'. Scan count 0, logical reads 6, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Item'. Scan count 1335, logical reads 32940, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'ObjectState'. Scan count 1, logical reads 10972, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Object'. Scan count 0, logical reads 20674, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Subject'. Scan count 0, logical reads 3293, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'FormDef'. Scan count 2, logical reads 70, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PrintedLabSampleLabel'. Scan count 0, logical reads 13144, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'PrintedForm'. Scan count 0, logical reads 4219, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'StudySite'. Scan count 0, logical reads 2756, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'StudyEvent'. Scan count 18, logical reads 40, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'StudyEventDef'. Scan count 0, logical reads 36, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'FormDefToStudyEventDef'. Scan count 1, logical reads 43, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'LabSampleDefToFormDef'. Scan count 1, logical reads 255, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Here is the statistics ion on 2000
Table 'LabTestToReportPanel'. Scan count 2123, logical reads 4820, physical reads 44, read-ahead reads 0.
Table 'LabReportPanel'. Scan count 130, logical reads 260, physical reads 0, read-ahead reads 0.
Table 'DiscreteValue'. Scan count 103914, logical reads 208214, physical reads 0, read-ahead reads 0.
Table 'Location'. Scan count 19031, logical reads 38062, physical reads 2, read-ahead reads 0.
Table 'Lab'. Scan count 19031, logical reads 38062, physical reads 0, read-ahead reads 0.
Table 'LabArea'. Scan count 19031, logical reads 38062, physical reads 0, read-ahead reads 0.
Table 'LabSampleDef'. Scan count 24670, logical reads 49340, physical reads 0, read-ahead reads 0.
Table 'LabTest'. Scan count 19406, logical reads 39575, physical reads 0, read-ahead reads 0.
Table 'LabReleasedSampleTest'. Scan count 4289, logical reads 73865, physical reads 1014, read-ahead reads 24.
Table 'Study'. Scan count 4291, logical reads 8582, physical reads 0, read-ahead reads 0.
Table 'LabSample'. Scan count 5647, logical reads 31382, physical reads 308, read-ahead reads 4.
Table 'Form'. Scan count 4291, logical reads 9272, physical reads 2, read-ahead reads 10.
Table 'PrintedLabSampleLabel'. Scan count 4289, logical reads 17097, physical reads 114, read-ahead reads 308.
Table 'ObjectState'. Scan count 6860, logical reads 13760, physical reads 1, read-ahead reads 0.
Table 'Object'. Scan count 6860, logical reads 23559, physical reads 90, read-ahead reads 701.
Table 'PrintedForm'. Scan count 1375, logical reads 4505, physical reads 40, read-ahead reads 16.
Table 'StudySite'. Scan count 1378, logical reads 2756, physical reads 4, read-ahead reads 0.
Table 'Subject'. Scan count 1599, logical reads 3332, physical reads 2, read-ahead reads 0.
Table 'StudyEvent'. Scan count 18, logical reads 52, physical reads 0, read-ahead reads 0.
Table 'StudyEventDef'. Scan count 18, logical reads 54, physical reads 0, read-ahead reads 2.
Table 'FormDefToStudyEventDef'. Scan count 1, logical reads 69, physical reads 0, read-ahead reads 23.
Table 'FormDef'. Scan count 2, logical reads 78, physical reads 1, read-ahead reads 4.
Table 'LabSampleDefToFormDef'. Scan count 1, logical reads 308, physical reads 1, read-ahead reads 306.
Table 'Item'. Scan count 1335, logical reads 36510, physical reads 140, read-ahead reads 1047.
(21234 row(s) affected)
(147 row(s) affected)
One difference between the two is the work table that 2005 creates versus 2000. I can attach the plans but they are huge. I will attach it if you ask.
What I was looking for was suggestions on what I could do short of rewriting code or any suggestions in general.
FYI, this has also been posted on the SQL Server Engine forum.
Thanks
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