SQL 2012 :: Deadlocking Under Repeatable Reads
May 5, 2015
Just migrated application from Oracle to SQL and we are seeing alot of deadlocking and blocking. I did notice that app seems to be passing isolation level of repeatable read. Attached is a .doc of one of the deadlocks, is there a way to avoid these in the repeatable read isolation level? This example is a select with two tables, using NCI's that cover the where, and a insert doing just a clustered index insert. Is this simply try to get rid of the repeateable read if not needed, guess have to check with vendor on that or is there a way to get this to not deadlock using repeatable read?
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Aug 19, 2015
Is the SQL Server Profiler Reads Column Incorrect For Parallel Plans?
I often use profiler as one tool to identify bad plans. The reads column gives me a good indication of excessive IO to dig into and correct if necessary. I often use it with Showplan so I can see what a query does, replicate it and fix it.
However I have just lost some faith in it. I am looking at a poorly performing query joining five tables. A parallel plan has been generated and one table is being scanned (in parallel) due to a missing index. This table had in excess of 4 million rows in it. The rest hitd indexes well. However the entire query generates ONLY 12 READS.
Once corrected, a single processor plan is used. This looks really efficient and uses 120 reads. That looks the right figure to me.
Does the profiler only display one thread of a parallel plan perhaps? Or something else?
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May 9, 2007
hello all,
I'm strugeling for quite soem time and hoping to get your assistance:
facts:
We have a flat file source
each record has the same set of columns, let's call it "identifying columns"
each row can have after the identifying columns (but not all the records have it) a second set of columns, let's call it "detailed info".
the "detailed info" set can repeat itself several time for each record
We have a sql table destination
The row in the table should represent an "indetifying columns" record
sample record 1:
David | 1 | Rodeo Drive | 456 |
sample record 2:
Jeff | 2 |
sample record 3:
John | 3 | Sunny rd | 111 | Marvell str | 6
expected output in the table:
David | 1 | Rodeo Drive | 456
Jeff | 2 | null | null
John | 3 | Sunny rd | 111
John | 3 | Marvell str | 6
question: How do i import the data from the source file into the table, when i dont know in advance how many columns each record has? and how do i divide the sets of "detailed info" into different records in the db?
Thanks,
Eric
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May 8, 2002
I'm getting this error quite often at my site and I'm looking for a way to resolve it. Any help would be appreciated.
Thanks,
Jack
Microsoft OLE DB Provider for SQL Server error '80004005'
Your transaction (process ID #15) was deadlocked with another process and
has been chosen as the deadlock victim. Rerun your transaction.
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Jun 21, 2001
Hi all,
I was wondering how much of an overhead would Running this
trace (1204) have over the system. Will my perfomance
degrade significantly. If yes, by what percentage ???
The trace is 1204 to keep a watch on DeadLocking
I am running this command
C:mssql7innsqlservr -T1204 /dc:mssql7datamaster.mdf
How much performance degrade are we talking about here ?
The Application is Peoplsoft and the db sizes is about 10
Gb !!
Regards
Girish
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Jun 14, 2004
I have a ColdFusion web application running on a SQL Server 7.0 back-end.
Within this application, there is are three queries in a row where the second query deadlocks 1-2 times a day, which is too high. The queries do the following:
1. Insert member details from a web form into member table
2. Select ID (key) of what was just inserted into the member table
3. Update a third table with the member ID
As I said earlier, the 2nd query is the one that I see deadlocked in the ColdFusion error logs. I am unable to replicate the problem, so I have not been able to troubleshoot using the procedures described in SQL-BOL (unless I am mis-understanding the documentation).
This sequence runs an average of 150 times per day, but it can be anywhere from 100 to 500 times, so the failure rate is about 1%.
Any ideas on why this is happening and what I can do to prevent it?
Thanks,
Cybermud
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Oct 2, 2014
We would like to benchmark our logical reads daily to show our improvement as we tune the queries over time.
I am using sys.dm_exec_query_stats summing the Physical and Logical Reads. Is this a viable option for gathering this metric? Is this a viable metric to gather?
select sum(total_physical_reads) as TotalPhyReads, sum(total_logical_reads) as TotalLogReads from sys.dm_exec_query_stats;
How best to provide performance based metrics.
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Apr 4, 2015
I am inserting updating few tables from snapshot and reading same bunch of tables from reporting using readcommitted . It is showing some deadlocks i think it is write in this situation as " x" is not compitable with "s" ,"is".
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Mar 25, 2008
Hi!
I was assigned to solve performance problems for an application. I fired up Sql Server profiler and started a trace. Downloaded Sql Server Trace Analyzer. It's a trial version so it's very limited. What I found is that one stored procedure generates almost 400 000 reads everytime it's used and it's used everytime the user wants to see his orders. I've tried to translate the t-sql to english from swedish, it looks something like this:
select top 100
o.orderid,
o.name,
o.latestdeldate,
os.name as OrderStatus,
os.orderstatusID,
p.placeID,
p.name as place,
p.address,
p.city,
a.name as worktype,
noOfActions=(select count(*) from actions a where a.order_orderid=o.orderid),
noOfServiceObjects = (select count(*) from Serviceobject s, Actions a where s.Place_PlaceID = o.Place_PlaceID and a.order_orderid = o.orderid and a.Serviceobject_serviceobjectid = s.serviceobjectid),
...
...
...
It has 8 select count(*) in the select statement then in the where statement it has 2 more select count(*).
I know it's very difficult for you to come up with a solution but do you know a better way than to use select count(*) everywhere? The count is used for to show different status flags on the website.
/Magnus
Jesus saves. But Gretzky slaps in the rebound.
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Aug 1, 2001
If I'm doing a dirty reads and a someone updates a record when I'm trying to read it is it possible to read both the old and new records thereby retrieving two records?
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Oct 30, 2006
How can You find the reads and writes per second of your hard drives in sql. I am reading my SQL book and it says that your average disk should have 125 or less i/o's. And it gave the forumal but as mentioned I don't know how to find the reads and writes.
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May 1, 2008
server: QAT on clustering server ----> 23 seconds
----------------------------------------------------
SS 2000 developer edition SP4
win NT 5.2 (3790) SP4
MeM 7935 MB
processors 4
root directory C:program files...
use a fixed memeroy size 640 MB
reserve physical memory for sql server
minimum query memory 1024 kb
use all available processors
minimum query plan threshold for considering 5
PROFILER READS = 5234
server: MILLER ----> 3 seconds
----------------------------------------------------
SS 2000 developer edition no service pack
win NT 5.2 (3790) SP4
MeM 2047 MB
processors 4
root directory f:MSSQL$INAQAT
dynamically configure sql server memory
use all available processors
minimum query plan threshold for considering 5
PROFILER READS = 598
----------------------------------------------------
Making story short. I got an application that hits only 1 database called RECORDS. I'm getting different duration when running an application. 23 and 3 seconds.
Same database, same objects and same application.
SERVER QAT is our staging server, means lots of databases
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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Jul 18, 2006
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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Jun 20, 2007
Hello,
im using sqldatareader to read my data and whenever time i loop through the reader it starts from second row why is that?
here is my code:while (reader.Read()){hinfo.Name = reader["_name"].ToString();hi.Add(hinfo);}
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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May 31, 2006
I have a set of triggers that log the history of changes to a table - i.e. I record inserts, updates, deletes (pretty standard audit stuff I suppose). I want to also log reads on that data. If I were using sprocs for reading data, this would be relatively painless, but I am using an O/R mapper to handle my data access, which writes dynamic sql at runtime (and I don't want to use sprocs with it) and then sends it down to the DB. Is there a way I can intercept reads and log them to the same table I am logging other actions? I know very little about the new capabilities of SQL Server 2005, but I would think I could somehow, maybe via the new CLR capabilities or similar, get access to these types of events within the database? Anyone? I know I could always do this higher up in the application layers, but I would like to keep all of this at the database level if possible....Thanks,
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Jan 17, 2002
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.
What SQL configuration parameter(s) should I check/modify to insure that the database is performing at it's optimun during these bursts?
Thank You in advance.
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Jul 21, 2000
Is there a way to get a total count of all SELECT, UPDATE, DELETE and INSERT statements to a SQL Server 6.5 database during a 12 hour period? I'm thinking maybe someone knows of a software that reads the log or monitors the server... I've been looking at the performance monitor and, although it has good information, it doesn't capture DML's.
FYI - it's for capacity planning.
TIA,
Mike
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Aug 24, 2007
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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Mar 5, 2008
GUys,
Is there any way track tables which have most no of reads and writes from a database of 400 tables.
Thanks
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Jul 27, 2007
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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Aug 28, 2006
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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Sep 19, 2006
I have written a same stored proc in TSQL and SQL CLR which basically takes an input xml and returns xml document. In SQL Profiler, I am getting reads value about five times more for the CLR. Does anyone has any idea why the CLR is doing more reads than TSQL? Thanks in advance.
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Dec 22, 2000
Hi Everybody,
One of my friend asked me "How do we reduce the query logical, scan reads
in SQL Server?".
I really don't know, how to answer him.
Can anybody explain me regarding this.
thanks,
Srini
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May 2, 2007
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
Audit Logout.Net SqlClient Data ProviderloginName3764129784 3146 156
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Jul 23, 2005
I am running a profiler trace against a database and noticed that thereads column always shows 0. When running the same trace againstanother machine I get back values in the reads column. I took a querythat profiler reported as having 0 reads and ran in in query analyzerwtih STATISTICS IO on and confirmed that there are in fact reads:Table 'tt_cawardalloc'. Scan count 1, logical reads 8, physical reads0, read-ahead reads 1.Table 'tt_clineitem'. Scan count 10, logical reads 125208, physicalreads 1540, read-ahead reads 2995.Table 'tt_contractitem'. Scan count 32, logical reads 676, physicalreads 0, read-ahead reads 0.Table 'tt_contract2'. Scan count 3, logical reads 121, physical reads4, read-ahead reads 0.I am on SQL 2000 sp3a. Any help appreciated.Thanks!
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Apr 17, 2007
I'm running the same query on two different PCs and tracing results in Profiler on my PC. When executing the query on PC1 - the total number of reads is 200000. When executing the same query on PC2 - the toal number of reads is 13000. It is almost 15 times more reads when executing query on PC2. The executed query is same on PC1 and PC2. Any reason for this?
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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Apr 17, 2008
Problem Statement........
Lets say user A accesses a record and is making an update to a column... next user B accesses the same record and makes an update to the same column and saves the data... how can user A check to see if an update has been made to prevent overwriting the data..
Is there a query statement that user A can write to check for this?
I understand locking can be used to prevent this but is there an alternative to locking.
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Jun 2, 2008
I ran Sql profiler and got the following results for a stored procedure
CPU of 1078;
Reads of 125464
writes of 0
Duration of 1882
how do i interpret the above results.
also what CPU and Duration is considered high and indicating a poor performing query.
I am using SQL Server 2005. Thanks
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May 5, 2015
Why is there often such a dramatic discrepancy between the logical reads recorded in the trace file versus the output of STATISTICS IO?
In the server-side trace I have running I found a reporting procedure that shows having 136,949,501 reads (yes, in hundreds of millions), and it's taking 13,508 seconds to complete.
So I pull the code from the trace and execute it via SSMS - it runs < 1 second, and only generates about 4,000 reads (using various different parameters I get the same result)
The execution plan shows nothing unusual
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Nov 5, 2015
How can I measure the disk reads and writes to see if I need to add aditional disks to the server?
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Dec 1, 2005
All my queries are being blocked while the tables are being replicatedand it is causing some 2 minute blocking. Is there a way for theReplication to allow dirty reads because I really don't care aboutthat, I would rather have dirty reads than 2 minute waits.Thanks.
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Dec 12, 2005
How do I determine which method I should use ifI want to optimize the performance of a database.I took Northwind's database to run my example.My query is I want to retrieve the Employees' Firstand Last Names that sold between $100,000 and$200,000.First let me create a function that takes the EmployeeIDas the input parameter and returns the Employee'sFirst and Last name:CREATE FUNCTION dbo.GetEmployeeName(@EmployeeID INT)RETURNS VARCHAR(100)ASBEGINDECLARE @NAME VARCHAR(100)SELECT @NAME = FirstName + ' ' + LastNameFROM EmployeesWHERE EmployeeID = @EmployeeIDRETURN ISNULL(@NAME, '')ENDMy first method to run this:SELECT EmployeeID, dbo.GetEmployeeName(EmployeeID) ASEmployee, SUM(UnitPrice * Quantity) AS AmountFROM OrdersJOIN [Order Details] ON Orders.OrderID =[Order Details].OrderIDGROUP BY EmployeeID,dbo.GetEmployeeName(EmployeeID)HAVING SUM(UnitPrice * Quantity) BETWEEN100000 AND 200000It's running in 4 seconds time. And here are theStatistics IO and Time results:SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server parse and compile time:CPU time = 17 ms, elapsed time = 17 ms.(3 row(s) affected)Table 'Order Details'. Scan count 1, logical reads 10,physical reads 0, read-ahead reads 0.Table 'Orders'. Scan count 1, logical reads 21,physical reads 0, read-ahead reads 0.SQL Server Execution Times:CPU time = 3844 ms, elapsed time = 3934 ms.SQL Server Execution Times:CPU time = 3844 ms, elapsed time = 3935 ms.SQL Server Execution Times:CPU time = 3844 ms, elapsed time = 3935 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 0 ms.Now my 2nd method:IF (SELECT OBJECT_ID('tempdb..#temp_Orders')) IS NOT NULLDROP TABLE #temp_OrdersGOSELECT EmployeeID, SUM(UnitPrice * Quantity) AS AmountINTO #temp_OrdersFROM OrdersJOIN [Order Details] ON Orders.OrderID =[Order Details].OrderIDGROUP BY EmployeeIDHAVING SUM(UnitPrice * Quantity) BETWEEN100000 AND 200000GOSELECT EmployeeID, dbo.GetEmployeeName(EmployeeID),AmountFROM #temp_OrdersGOIt's running in 0 seconds time. And here are the Statistics IOand Time results:SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 0 ms.Table '#temp_Orders0000000000F1'. Scan count 0, logicalreads 1, physical reads 0, read-ahead reads 0.Table 'Order Details'. Scan count 830, logical reads 1672,physical reads 0, read-ahead reads 0.Table 'Orders'. Scan count 1, logical reads 3, physical reads 0,read-ahead reads 0.QL Server Execution Times:CPU time = 15 ms, elapsed time = 19 ms.(3 row(s) affected)SQL Server Execution Times:CPU time = 15 ms, elapsed time = 19 ms.SQL Server Execution Times:CPU time = 15 ms, elapsed time = 20 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 1 ms.(3 row(s) affected)Table '#temp_Orders0000000000F1'. Scan count 1,logical reads 2, physical reads 0, read-ahead reads 0.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 3 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 3 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 3 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 0 ms.By the way why "SQL Server Execution Times"exists 3 times and not just one time?Summary:The first code is clean, 1 single SELECT statement buttakes 4 long seconds to execute. The logical reads arevery few compared to the second method.The second code is less clean and uses a temp table buttakes 0 second to execute. The logical reads are waytoo high compared to the first method.What am I supposed to conclude in this example?Which method should I use over the other and why?Are both methods good depending on which I prefer?If I can wait four seconds, it's better to reduce the logicalreads in order to provide less Blocking on the live tablesin a heavily accessed database?Which method should I choose on my own database?Calling a function like dbo.GetEmployeeName getsprocessed per each returned row, correct? That meansIf i had a scenario where 1000 records were to be returnedwould it be better to dump 1000 records to a temp tablevariable and then call a function to process each recordone at a time?Or would the direct approach without usinga temp table cause slower processing and moreblocking/deadlocks because I am calling the functionper each row as I am accessing directly from the tables?Thank you
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Aug 1, 2006
Is it possible to find the reads/writes to a sql server table ?
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