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STATISTICS IO: Scan Count Vs Logical Reads


Hello

I'm doing som performance research, I have a index with following priority: ClientId, Active, ProductId. Active is a bit field telling whether the Product is active or not, it can be inactive products than active, but always at least one active product.
When I'm executing



SELECT * FROM [table] WHERE ClientId = [id] AND ProductId IN (1,2,3,5,7,9,20)

I'm getting following result: Scan count 1, logical reads 490

 

When I'm leading SQL Server to the right paths by including the to possible values in Active by executing the following SQL:


SELECT * FROM [table] WHERE ClientId = [id] AND ProductId IN (1,2,3,5,7,9,20) AND Active IN (0,1)

I'm getting following results: Scan count 14, logical reads 123

 

With this information, which version would you say is fastest and why?

When I was running this query 1000 times with different ClientId I got a average time of 172 ms for the first query, and 155 ms for the second one. I have been told that scan count is very expensive... out of this example it seems that the cost of 1 scan count is like 20 logical reads?


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PS There are 60,078,605 rows in the table
 
Please help!
 
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SERVER MILLER is just a server i just assembled, means just one database (RECORDS).

Not sure if it's because it's a clustering server that is causing the issue nor the reads. If its the reads, what is causing it? Do you think is the how the memory is configured?. Will the experts pls stand up?

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So I€™m at a dead-end looking for the reason behind the following behavior. Just to make sure no one misses it, the 'behavior' is the difference in the number of reads between using sp_executesql and not.
 
The following statements are executed against a SQL 2000 database that contains >1,000,000 records in the act_item table. They are run using Query Analyzer and the Duration and Reads come from SQL Profiler
 
SQL 1: 
exec sp_executesql N'update act_item set Priority = @Priority where activity_code = @activity_code', N'@activity_code nvarchar(40),@Priority int', @activity_code = N'46DF335F-68F7-493F-B55E-5F9BC6CEBC69', @Priority = 0
 
Reads: ~22000
Duraction: 250-350 ms
 
SQL 2:
DECLARE @Priority int
DECLARE @Activity_Code char(36)
 
SET @Priority = 0
SET @Activity_Code = '46DF335F-68F7-493F-B55E-5F9BC6CEBC69'
update act_item set Priority = @Priority where activity_code = @activity_code
 
Reads: ~160
Duration: 0 ms
 
Random information:

Activity_code is an indexed field on the table, although it is not the primary key. There are a total of four indexes on the table, none of which include the priority as one of the fields.
There are two triggers on the table, neither of which is executed for this SQL statement (there is an IF UPDATE(fieldname) surrounding the code in the trigger)
There are no foreign relationships
I checked (using perfmon) to see if a compilation/recompilation was happening. No it's not.
 Any suggestions as to avenues that could be examined would be appreciated.
 
TIA
 

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i look at the database and i have two rows but its reading only the second row, skiping the first row 
 

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SQL 6.5 - 5.5 Gig
NT

Hello,

Throughout the day our Document Management application generates high busts of physical page reads when users query the database.

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Thank You in advance.

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I'm trying to insert all the rows from a table to a new table.
(insert A select * from AA)
The reads on Profiler shows ar really high value (10253548).

First I created a unique clustered index and the reads shows (3258445), then I created a non clustered index expecting to have lower reads. Instead the reads shows (10253548).

I read creating indexes helps reduce reads. But it's not happening.
Any ideas what is going on?

=============================
http://www.sqlserverstudy.com

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Thanks

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Hi,
 
Can any of can explain, what the "Reads" column in Profiler exactly mean ?  I'm not comfortable with the explanation given in BOL.
 

"The number of read operations on the logical disk that are performed by the server on behalf of the event. These read operations include all reads from tables and buffers during the statement's execution"
 
For the same procedure with same parameters, if the server is not loaded much, the Reads are in a few hundreds, but when there are more than 1000 concurrent users, why it is going to millions ?  What other parameters affecting this reads ? And how can I reduce it ?
 
Environment: SQL Server 2005 64-bit Enterprise Edition on Windows Server  2003 R2 Server x64 Enterprise Edition SP2

 
Thanks in Advance.
 
Regards
 
Babu
 

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Hi,

I have been seeing a basic scenario of a write transaction appearing to unexpectedly lock-out reading.

The database has isolation set to "READ COMMITTED".

The scenario is:

1.) Start a transaction (for doing a write)

2.) Do a read before the transaction (for doing the write) is committed (e.g. sqlCommand2.ExecuteReader()).

--> the code will appear to lock-up (then time out).

I see the same behavior if I step through the "write" code with the debugger (to a point after the transaction is started, but before it is committed), and run a "SELECT * FROM" type query from Microsoft SqlServer Management Studio.

Following is the code sample demonstates the issue.

Thoughts on how to resolve the issue (to let me do "read committed" reading of the database table)?

Thanks!

Andy 

 

 

 

Module Transaction

Sub Main()

Dim exception1 As Exception

Try

' Create/Open Database Connection

Dim sqlConnection1 As New System.Data.SqlClient.SqlConnection("Server=GRB-AB;Database=Transaction;Trusted_Connection=True;")

sqlConnection1.Open()

' Start transaction

Dim sqlTransaction1 As System.Data.SqlClient.SqlTransaction = sqlConnection1.BeginTransaction()

' Set Parent record

Dim sqlCommand1 As New System.Data.SqlClient.SqlCommand("INSERT INTO Parent (Name) VALUES ('ParentValue');", sqlConnection1)

sqlCommand1.Transaction = sqlTransaction1

sqlCommand1.ExecuteNonQuery()

' Get Id from parent record (note: this code assumes the table was empty when this program starts)

sqlCommand1 = New System.Data.SqlClient.SqlCommand("SELECT Id FROM Parent;", sqlConnection1)

sqlCommand1.Transaction = sqlTransaction1

Dim parentId As Integer = CType(sqlCommand1.ExecuteScalar(), Integer)

 

'

' Do reading test to test concurrently reading table being written to

'

' Create/Open Database Connection for reading test

Dim sqlConnection2 As New System.Data.SqlClient.SqlConnection("Server=GRB-AB;Database=Transaction;Trusted_Connection=True;")

sqlConnection2.Open()

Dim sqlCommand2 As New System.Data.SqlClient.SqlCommand("SELECT Id FROM Parent;", sqlConnection2)

sqlCommand2.ExecuteReader()

Dim i As Integer

While (sqlCommand2.ExecuteReader.Read = True) ' <===== LOCKS UP HERE **************

i = i + 1

End While

'

' End reading test

'

 

' Set child record

sqlCommand1 = New System.Data.SqlClient.SqlCommand( _

"INSERT INTO Child (Name, ParentId) VALUES ('ChildValue', " & parentId.ToString & ");", sqlConnection1)

sqlCommand1.Transaction = sqlTransaction1

sqlCommand1.ExecuteScalar()

' Either 1.) commit transaction OR 2.) rollback transaction

Dim test As Boolean = False

If test = False Then

sqlTransaction1.Commit()

Else

sqlTransaction1.Rollback()

End If

sqlConnection1.Close()

sqlConnection2.Close()

Catch ex As Exception

exception1 = ex

End Try

End Sub

End Module

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Hi,

I'm trying to figure out why my sqlserver is flatlined on the CPU. I'm doing a trace and can't help but notice this, with crazy high reads. I'm not sure what this is? It doesnt look good to me, altho maybe its nothing. Any info is much appreciated.

Thanks again!
mike123



Event Class/ TextData/ApplicationName/ LoginName/ CPU/ Reads/ Writes/ Duration

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also what CPU and Duration is considered high and indicating a poor performing query.
 
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I'm trying to analyse that query and reduce the number of logical reads as it's is too high but then I get completly different result on different PC.

 

Thanks.

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Problem Statement........
 
 
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I understand locking can be used to prevent this but is there an alternative to locking.

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What is happening here? Where should I look to solve this problem?

 

Thanks

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Brian
 

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All other software on the machine works normally, and nothing else seems wrong.

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System.Data.SqlClient.SqlError: This differential backup cannot be restored because the database has not been restored to the correct earlier state. (Microsoft.SqlServer.Smo)

 

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Object ((D4000).(dbo).(shipstop)as (A))


update drivers set dr_miles_run = case when D1.miles > 0 then d1.miles else 0 end
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and mf_manifest_nbr = B.ss_manifest_nbr
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and B.ss_stop_type in ('DT','RD')
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IE:

D:Logsfile1.log
D:Logsfile2.log
D:Logsfile3.log
D:Logsfile4.log

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Jeff

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