Managing Concurrency
May 15, 2007
I want to centralize my previous standalone application. Previous application was using VB.NET and Access XP. Now I want to keep a centralized database (SQL Server 2005) and VB.NET 2005. At this point of time thousands of concurrent users will connect to the database at the same time.
In my application, when a ticket is being issued to a tourist, an SQL query finds the max(ticketno) for the current month from the main table and reserves this number for the current ticket. When the operator has finished entering information and clicks SAVE button, the record is saved to the main table with this ticket no. Previously there was no issue since the database was standalone.
I want to know how to block the new ticket no so that other concurrent users are not using the same number for saving a record. How to better tune the database for thousands of concurrent users at the same time? I also want that the other user must not get an error message when he attempts to save a record. It should be automatically handled by the database.
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Oct 25, 2006
Hi everybody,I need to understand how concurrency excatly
work in asp.net. For example, I'm confused what happens if two users at
the same time try to access the same record in a table or even the same
variable. Do ASP.NET handle this , I mean by locking one user and
letting the other to have access OR it's up to the programmer to write
some code to lock shared resources such as database , objects and
variables?If it's up to the programmer to do this task, I appreciate if you can show me an example that clarifies that.Thank you
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Jul 23, 2005
Following on from a thread I started about "concurrency" (real-time-ishsystem), I thought I would play about to see if I could easily adapt my datamodel to take account of potential multi-user write conflicts. So, I wouldappreciate you checking my logic/reasoning to see if this kind of thingwill work. Below I have a stored procedure that will simply delete a givenrecord from a given table. I have appended a "_Written" counter to thecolumns of the table. Every time the record is written, the counter isincremented. Clients store the current _Written count in their objects andpass this in to any write procedure executed.The procedure explicitly checks the _Written count within the transaction tosee if it agress with the written count passed in by the client. If it doesnot, the client throws an error. Note I am explicitly checking the_Written count precisely so I can determine exactly why this operation mightfail, rather than checking @@ROWCOUNT after an update.Thanks.RobinCREATE PROCEDURE dbo.proc_DS_Remove_DataSet@_In_ID INTEGER,@_In_Written INTEGERASDECLARE @Error INTEGERDECLARE @WRITTEN INTEGERBEGIN TRANSACTIONSET @Error = @@ERRORIF @Error = 0BEGINSELECT @WRITTEN = _Written FROM MyTable WHERE ID = @_In_IDSET @Error = @@ERRORIF @WRITTEN <> @_In_WrittenBEGINRAISERROR ('10', 16, 1)SET @Error = @@ERRORENDENDIF @Error = 0BEGINDELETE FROM MyTable WHERE ID = @_In_IDSET @Error = @@ERRORENDIF @Error = 0COMMIT TRANSACTIONELSEROLLBACK TRANSACTIONRETURN @Error
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May 27, 2007
Do single commands (or stored procedures) execute concurrently, or they are executed one by one. How do you perform a lock during the execution of a command (or stored procedure).
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Jul 5, 2004
Hi,
I have a page that shows some problem indexes (cards ? I don't know the word :/ ) and I want to show only those that are from the current day.
I'm using SQL server 2000. I have a date field inside my table (datetime type). So I tried to put another condition in my WHERE clause. This is:
WHERE something = something else AND mydate = DATEPART('dd', getdate())
or
WHERE something = something else AND mydate = DAY(getdate())
Both don't work..
I wonder if I can really use this in a WHERE clause...of if I'm using them correctly.
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Feb 7, 2001
Does anyone know if it's possible to grant a user the ability to manage jobs in server agent besides giving them SA rights? I none of the server roles beside SA seem to be able to work.
Thanks
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Aug 16, 2004
Hello,
I am currently working on a large project that will be developed using MS SQL. I have been considering two options when it comes the creation of the database. The first option is to create a sepereate table for each of my clients. The tables would be labeled by their Id number then the tables reqular name. Fore example : 781_Users.
The other option is to create a different database for each of the clients.
I just need the data to be seperated between clients, it cant mix. Please just give me your opinion on which option you would consider if you were operating a large project.
Thanks in advance!
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Sep 27, 2004
Has anyone experienced any limitaions or concerns for managing SQL 2K remotely using remote desktop, pleased advise.
Thanks
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Jan 9, 2008
Hello everyone. Have a little situation here. I am not normally the DBA at my work, but i've been poking around a little with a SQL Server 2005 implementation. I'm pretty new to this, so please pardon my lack of knowledge.
This particular server is running a lightly used SQL server, or so im told. As part of my Sys Admin duties, I logged into the box today for some routine checks, only to be notified that I was running out of disk space (which is another story).
After poking around awhile, I see that my tempdb is almost 15gb in size.
I don't have a lot of experience with SQL Server 2005. I've worked mostly with 2000. I did read a few things where tempdb has changed a bit in 2005? I wasn't sure.
So I have about 10gigs of space free on my HD (I'm adding more space tomorrow) and I need to figure out what to do.
I came across this thread here:
http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=64914
is that something I should do? I'm a little concerned I might run out of space overnight and not make it in time.
Anyone have some suggestions?
Thanks.
TCG
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Jan 3, 2006
Hello,Has anyone ever come across a reason why someone would manually create auser table incl. permission flags and not use the inbuilt user/rolesprovided by that database? The only reason that stands out for me is tomake the database that bit more portable?Thanks,Craig.
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Sep 12, 2006
Hi everyone,I'm looking into moving my desktop system at work to Linux from WindowsXP, and one tool I've yet to find a suitable replacement for is MS SQLEnterprise Manager. I mainly need to query MS SQL databases fromLinux, and management tasks (monitor backups, services, etc) can bedone on the MS SQL servers themselves. THere was an application I usedto use on OSX which would connect to a variety of databases, includingMS SQL, and they had a Linux version of the client .. but can'tremember the name. But really any Sybase client that can connect to MSSQL with some ease will work.Thanks for any suggestions or ideas ...Alex
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Sep 5, 2007
Hello,I have an ASP.NET website which uses SQLServer 2000 as database. I am into tracking the customers who visit to the website. We are getting around 10000 users per day. When each page gives request, request details will be inserted into SQL tables.Table's I am using is indexed. I am in confusion that when these index will be regenerated ? Will it regenerated automatically when new row's are inserted ? or do we need to regenerate it manually ? And what is the difference on Clustured Indexing and Full text indexing ? Which one I should use for better performance ?Thanking youNavaneeth
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Jul 4, 2006
Hi everyone,
When an error occured in a transaction and we can also create a message for this error ourself too by using @@error in order to print a message . However, I wonder that is it possible to really catch and handle the error ??
For example, when error occured it makes the transaction terminated. So how can we prevent transaction from terminating ??
Meanwhile, I also examine RAISERROR statement but it also does not prevent a transaction from terminating instead şt only provide an additional message for the error.
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Jun 20, 2006
I have a user object that is stored in the session for each user but what if an administrator updates a certain user and I want to reflect the update to the user if they are logged in?One possible way of solving this is:Each time the user goes to a page, check the user table and compare the timestamp. That would mean if 30 users refresh the page..the db would hit 30 times lol. I don't think that would scale very well.Any ideas on how to solve this?
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Aug 4, 2006
I have a table where I count how many emails of a given type are sent out each day. This incrementing is wrapped in a sproc that either inserts a new row, or updates the existing row. The column that counts the value is named Count of type INT.
Below is the sproc, seems like a straightforward thing. However, I'm seeing email counts higher than they should be when there's a high number of concurrent executions of the sproc. I'm pretty sure it's not a problem in the calling code, so I'm wondering about the UPDATE statement, since it updates a column based on the value of the column. I would think this should work since it's wrapped in a SERIALIZABLE transaction, anybody have further insight?
SQL Server 2005 by the way.
Sean
CREATE PROCEDURE [dbo].[IncrementEmailCounter]( @siteId SMALLINT, @messageType VARCHAR(20), @day SMALLDATETIME) ASBEGIN SET NOCOUNT ON;
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE BEGIN TRANSACTION
IF (SELECT COUNT(*) FROM EmailCount WHERE SiteId = @siteId AND MessageType = @messageType AND [Day] = @day) = 0 INSERT INTO EmailCount (SiteId, MessageType, [Day], [Count]) VALUES (@siteId, @messageType, @day, 1) ELSE UPDATE EmailCount SET [Count] = [Count] + 1 WHERE SiteId = @siteId AND MessageType = @messageType AND [Day] = @day
COMMIT TRANSACTION SET TRANSACTION ISOLATION LEVEL READ COMMITTEDEND
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Feb 17, 2007
I'm wondering whether the following code would work if users are RAPIDLY registering (assumption) WITH the same username.public bool UsernamExists(string username)
{
string sql = "SELECT true FROM [users] WEHRE username = @username;";
return Convert.ToBoolean(comm.ExecuteScalar());
}
public bool Signup(User user)
{
bool usernameExists = UsernameExists(user.Username);
if( usernameExists ) return false;
//update or insert sql for user etc blah blah
} If two users try to signup AT THE VERY SAME TIME (DOWN TO THE NANOSECOND), would this technique work? Do I have to wrap it in a transaction, stored procedure?? Thanks.
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Jun 1, 2007
Hi,I'm trying to implement Optimistic Concurrency in asp 2 but so far it has caused me nothing but problems.First, when doing an UPDATE I tried to use the primary key & a timestamp field which I had in SQL Express.. VS 2005 generated the stored procedures fine however when it came to the actual updating I think there was a problem with the conversion of the timestamp field when it was being stored in a text box (in a FormView control). So.. as a result that failed. And also I checked sooo many places online and haven't been able to find any examples of code where a timestamp was used with success in asp2.Next, I got ride of the timestamp type (in SQL Express database) and used a datetime and then.. I just implemented Optimistic Concurrency by passing in ALL the values (ie all the original values) like is proposed http://www.asp.net/learn/dataaccess/tutorial21vb.aspx?tabid=63 . This... works however I really do not want to have to pass in ALL these values (ie original and new).Ideally I would like to be able to use the primary key & the datetime field to handle the Optimistic Concurrency checks where only the original values of both those fields are passed back into the stored procedure. Now.. I tried this as well, but I kept getting an error that suggests that (for some reason) the FormView or DataSource is passing ALL the values (original & new) into the dataset as opposed to only the original primary key & datetime fields & the new set of values.Can ANYONE offer any help? I really would like not to have to pass in all these values.Thanks in advance!
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Apr 6, 2005
Hi! I'm building a web application with ASP.NET, and using MS SQL 2000 for my database server.
How should I do to guarantee the integrity of the data in spite of the concurrent access? Meaning... how can I make sure that more than 1 user can update 1 table at the same time, while no error will occur? Do I need to add some codes at my aspx file? Or do I need to do something to my database? Or do I not have to worry about it?
Thank you.
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Sep 27, 1999
Can anyone help with concurrency issues. Small network and only one person at a time can log into the database.
It was originally written in MS Access and converted to SQL 7.0 with a VB front end.
Thanks,
Rick
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Feb 2, 1999
We have two processors on which sql server was installed.
SMP Concurrency opion is -1. and process priority is 0.
The computer is dedicated to Sql server.
with the same setup, has any body faces any problem....?
some times suddenly system hangs... sql sever takes 99% cpu usage ...
Shall I run the SQL Executive, SQL Performance Monitor with this setup...?
will it afect the system...?
[ this kind of setup - those you experienced.. ]
please reply immediately....
thanks
Wincy
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Mar 31, 1999
Hello,
SQL Server6.5 is installed on a dual processor computer. So can I make use of dual processors by setting SMP concurrency to -1 or 2.
I tried setting these values but failed to do so. Server is running at setting 1 always, irrespective of configured value.
Any suggestion???
Srini
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Sep 6, 2004
Is there any way to get the sample below working so that both "threads" are guaranteed to get unique and incrementing values?
I'm suspecting the answer is no. You can use transactions on completely database oriented operations that read/write to a database and complete. But there aren't complete synchronization controls for operations like below that try to return a value to an outside process.
IF OBJECT_ID('SimpleTable') IS NOT NULL
DROP TABLE SimpleTable
CREATE TABLE SimpleTable (
A INTEGER
)
INSERT INTO SimpleTable (A) VALUES (1)
-- Run in one window
DECLARE @value INTEGER
BEGIN TRANSACTION
SELECT TOP 1 @value = A FROM SimpleTable
WAITFOR DELAY '00:00:05'
UPDATE SimpleTable SET A = @value + 1
COMMIT TRANSACTION
SELECT @value
SELECT A FROM SimpleTable
-- Run in a second window
DECLARE @value INTEGER
BEGIN TRANSACTION
SELECT TOP 1 @value = A FROM SimpleTable
UPDATE SimpleTable SET A = @value + 1
COMMIT TRANSACTION
SELECT @value
SELECT A FROM SimpleTable
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Oct 5, 2006
Suppose process A is updating record #1 in table T.
By default, can other processes read record #1 while the updating is in progress ??
If the answer is Yes, then which value can they see - the old one or the new one ?
Thank you in advance.
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Aug 16, 2006
Did I understand correctly the Pesimistic access:
When we choose pessimistic access
-we lock all the rows of the table. right.
-other users still can access the table if they specify read only mode meaning if their intention is to only read the data and not modify it. am I right
Thanks for your help.
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Sep 21, 2006
In a previous post, the theme of cursors and concurrency was touched as a secondary subject. I have a specific question about it as the primary one:
if we have
--------
create proc myProc
as
declare cursor for
select * from mytable
go
----------
if two or more clients(webpages for example)
execute myProc concurrently will the cursor be safe ? or would I have to make special arrangements, there are a couple of procs (that use cursors)that somebody else did and would not like to modify but we want to make the procs web available,
thank you
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Aug 4, 2005
hi gurusthe scenarioFrontend - MS Access (not yet decided whether MDB or ADP)Backend - MS SQL Serverit is a conversion from MS Access backend to MS SQL Server Backend.Planning to create stored procedures for all the Inserts, Updates,Deletes and Business Rules / Validations wherever it is possible.the problemi am running in concurrency problem. the same classic scenario of twousers retrieving the same row (record) from the same table. it allowsboth the user to update the record, that is, the user who updates lasthas his changes saved though he retrieved that particular recordsecond.what i need is that the user who retrieved the record second shouldn'tbe able to update or delete the record when it is already retrieved byany other user.would appreciate if someone pointed me in the right direction to solvethe above problem, i know it is related to isolation property but amnot surethanx in advanceregardsbala
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Apr 6, 2006
Hi,
I was wondering if it is possible to call a stored procedure from sql server 2005 (call it sp_1) that calls an assembly which takes a message, wraps it in soap and calls a webservice and waits for a reply from that webservice (the stored procedure is clr not t-sql). This WebService needs to then call sp_1 to perform some other tasks. Is this possible or does sp_1 need to have finished what it was doing before it can be called again.
I have been trying to do this and have received a number of errors one of which looks like;
'The context connection is already in use.'
Sorry if I haven't worded it very well, I will try to clear up any questions if you need me to.
Thanks
N
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Mar 5, 2008
I created an ETL Process which loads four different types of files into different tables in parallel. There is no issue with this parallelism as the sources and destinations are distinct. But I have a common log table where I log the status and timings of each load for any file type. When ever I start a new file load, I create an entry in this log table with the FileTypeID and LoadInProcess as 1 (this will be set to 0 for all other records of the same file type). At different stages of the load, I will pull the active LoadID of the current file type and update the same record with the timings and results. My code looks like this -
Code Snippet
SELECT
@LoadLogKey = LoadLogKey
FROM
SystemLoadLog (NOLOCK)
WHERE
FileTypeID = 1 and LoadInProcess = 1
IF @LoadLogKey is NULL
RAISERROR('Unable to retrive LoadLogKey for the current load!')
***Process1 Query
***Process2 Query
***Process3 Query
UPDATE
SystemLoadLog
SET
Process1Result = x,
Process2Result = y,
Process3Result =z
WHERE
LoadLogKey = @LoadLogKey
The first SELECT query is giving problems as different processes are using the same table to log the results and timings. The source files I load are too small that the data load finished in 1 or 2 seconds most of the time and within this timespan, I update the log atleast 10 times. So, if four different file types are loading, the hits to the SystemLoadLog can be as bad as 20 to 30 times in 1 second.
Can anyone let me know how to handle this?
Thanks in Advance!!!
Harish
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Dec 4, 2006
Hi:
Need some advice. Here is the scenario:
There are 17 Client PC connected to a Server with SQLExpress 2005.
17 Client will do verification of identity before sending data to display at server
in first in first out basis using Datagridview ( the earliest data received will be
display first) and stored for review at later stages.
What should I do? I plan to use VB2005 after trying the EXpress.The Tasks are simple:
Data send --> Server Diplay and Stored---> Someone at Server will Acknowledge by
Button--> Messages will be sent to inform Client data received.
I could have 17 different Table (But with same fields!) and displaying the Data send
by reading all 17 tables and display it with Datagriedview. But this definately will
be slower than Just read from 1 table!
I'm concerned about Concurrency as there is chances that May be more than 1 user
might trying to update the Database at the same occasion. Can someone provide me a
Tips and advice?
Note: I had came across something call CurrencyManager which is related to
Concurrency, Not quite sure about what is this
Thanks
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Jun 26, 2007
I've combed through SQL Help to find the answer to my question but I think it's telling me it can't be done. I work both from an office with my servers and from home. When I'm at home I would like to access my SQL server remotely using a tool such as MS SQL Server Management Studio. But it appears there is no way to access my SQL Server for management purposes using Management Studio over a remote internet connection. I can access the server using Management Studio while I'm on the internal office network but not from home.
Has anyone been able to do this or might recommend a third party tool as robust as Management Studio?
Thanks
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Nov 25, 2005
HiI'm trying to access the properties of my datasource programatically so I can change the stored procedure it connects to depending on the value of a querystringIn my page load I have
Dim myMode = Request.Params("mode")Select Case myMode Case "Category" sqldatasource1.SelectCommand = "productsbycategory" sqldatasource1.SelectCommandType = SqlDataSourceCommandType.StoredProcedure ******'Need to add querystring parameter Case "Wishlist" sqldatasource1.SelectCommand = "productsbywishlist" sqldatasource1.SelectCommandType = SqlDataSourceCommandType.StoredProcedure ******'Need to add Session variable parameter Case Else sqldatasource1.SelectCommand = "allProducts" sqldatasource1.SelectCommandType = SqlDataSourceCommandType.StoredProcedureEnd SelectThe problem that I have is that I need to pass a parameter to the first 2 procedures above, a querystring to the first and a session variable to the second.How do I add parameters programaticallyMany thanks
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Jan 2, 2006
Hi, I just start using MSSQL server 2005, I already install vss studio
2005 so SQL server 2005 is already installed by default (express
edition).
But unlike SQL server 2000, I coultn't find any tools similiar to "sql
entreprise manager". I was able to create a new database only from
server explorer tools in VSS. But pretty strange that this database act
like a microsoft access database (creating a database file on my
app_data folder). (I am sorry I am new in SQL server 2005
ExpressEdition ).
My question :
1. is that (above) really how mssql server 2005 works?
2. how to create a new user for this database? (example user: sa password: "admin")
thanks
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Apr 25, 2001
Does anyone have any pointers or suggestions in explaining this topic?
The topics are what's including: Managing Transactions, SQL Server Locking and Managing Locks.
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