Multi-user Concurrency
May 30, 2006
Does anyone have links to various strategies for handling multi-user concurrency issues when updating data in SQL Server (2000 or 2005), either in the database (stored procedures) or via code.
I've seen a couple such as:
Check individual user updated columns to see if the database columns have changed and if not apply the updated columns (either individual updates or constructing a dynamic SQL statement).
Check all the fields for any change and if no change, update all the fields.
Check a version field for change and if no change, update all the fields.
What I haven't seen is complete solutions such as for the first one, ensuring the record is locked and can't be changed while checking for concurrency and ultimately updating the data. For the second one, how to raise an error if there was a problem, or for the third one how to ensure the record is locked between the version check and the update.
Even pieces of solutions are welcome (locking records, testing for change, etc). Just want to compare and contrast various methods as I create an infrastructure for 2005.
Thanks,
LarryC
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Feb 6, 2004
I'm currently looking at a multi-user app that has an Access 97 frontend and an SQL2K backend. Proposed changes to the system mean that the user concurrency count is likely to increase dramatically, and I'm wanting to know if there are any limits to the concurrency for this architecture.
Any experiences/help appreciated.
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Aug 3, 2006
Hi to all DBAs,
I would like to ask if there will be a write and concurrency issue if i would create an online application with just one user connecting to the database, just like most open source php/mysql that can be downloaded
i.e
Setup 1. I will grant a single user that will connect to a database and will be set to a config.inc.php file and then create a table users (userid, username, password) and this table will be used for the application authentication and access control.
Setup 2. or is it much better to grant users that will connect to the database and have the table users for access control of the application?
to further illustrate my query:
Setup 1 would be:
###################Table: Users
user a@ipadd --> db1 --> userid mary --> myOnlineApp
user a@ipadd --> db1 --> userid john --> myOnlineApp
user a@ipadd --> db1 --> userid paul --> myOnlineApp
and Setup 2 would be:
#####################Table: Users
user mary@ipadd --> db1 --> userid mary --> myOnlineApp
user john@ipadd --> db1 --> userid john --> myOnlineApp
user paul@ipadd --> db1 --> userid paul --> myOnlineApp
will Setup 1 be enough if I will use SQL Server as database?
or Setup 2 is better user/database architecture?
This application will be online enrollment for a school with 16,000 students
very much appreciated for the feedbacks and suggestions
^_^x
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Feb 27, 2008
I am using SharePoint Services 3.0 (SP1) with default configuration options, which installs the Microsoft##SSEE instance of SQL to my local C: drive.
While attempting to relocate the files to another drive, I set one of the databases (as recommended) to Single User by using the SQL Server Management Express tool.
I cannot now reset that database to Multi User, even by executing the query
exec sp_dboption 'database_name', 'single user', ''FALSE'
again by using the Management Express Tool.
Can someone please help, in plain english???? Thanks
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Jun 21, 2004
I have written a VB/SQL Server based application. The application uses stored procs and the SQL Server security model to handle logins and permissions. My partner and I want to sell the applicaiton to specific businesses and offer a rental program for smaller companies that would like to use the application to connect to an internet based database. The application uses TCP/IP with a specific port number to connect to the database so it can be used in or out of LAN.
If we rent the application, maintenance is simple. I just create a user in the database with the login/password the user would like and viola they have access to the data.
When a company wants to purchase the program to use in-house, we would like to offer two alternatives: #1 a single user or #2 a multiple user SQL Server database.
My question is if a company purchases the single-user version, how can we keep them from adding users to their database. In other words, since we have no control over the database at the client's location, how can we ensure that it remains a single-user database?
Thanks for any help!
Randall Medcalf
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Dec 5, 2007
Dear all,
to restore one perticular backup set, i've made the database to single user mode, now it is not accepting me to connect to that again...
how can i bring the database to multiuser mode?
thanks in advance
Vinod
Even you learn 1%, Learn it with 100% confidence.
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Nov 5, 2007
Can multiple users connect to SQL Server 2005 concurrently?
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Feb 7, 2008
Dear All,
i've altered my database to single user mode. and now trying to change to multi user mode with the query
alter database mydb set multi_user
but it is saying that it is in single user mode. query analyser closed.
how can i change that to multi user mode? idont know who opend that
to run sp_who it is not showing the database in dropdown list in enterprise manager.
thanks in advance
Vinod
Even you learn 1%, Learn it with 100% confidence.
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Apr 16, 2008
I've taken over development of a Vs2003(vB)/MsSql2000 application which usually runs in on a Windows 2000 server with multiple workstations running the application simultaneously in Remote Desktop Sessions.
The central user interface element of the application is an un-databound grid (actually a farpoint spreadsheet) which displays sql table rows that are accessable from every workstation. The grid refreshes its content whenever a specific subroutine is called. That subroutine performs a query which loads its results into a collection which is then loaded into the grid. The subroutine is called during startup and at other times using the rather elaborate mechanism described below. Each workstation also has the ability to modify any row in the grid via a dialog-based editor. The grid itself is not setup to allow inplace editing.
The grid usually contains about 200 records and 20-50% of these records get modified (some repeatedly) every hour.
My question involves the classic multi-user issues of keeping all of the seperate workstation's grids current as individual workstations make modifications to the data.
What is Microsoft's recommended method for handling multi-user data-refresh requirements in custom applications written in VB.NET2003 with MsSQL2000?
Now that you know what I'm looking for, let me add a little more detail. The existing code handles this multi-user refresh issue in the following way...
A SQL Trigger is attached to the SQL Table's Insert/Modify and Delete events. That Trigger calls the xp_logevent built-in stored procedure to make an entry in the NT Event Log.
The application contains a subroutine to handle EventLog("Application").EntryWritten messages. That subroutine calls the subroutine (mentioned earlier) which refreshes the grid contents through a new SQL query.
In this way, whenever any workstation changes the table data, a trigger fires which makes a log entry and broadcasts an EntryWritten message into the global windows environment. The individual applications (each running in their own RDP session) hear the message and respond by refreshing their grid.
This all seems a little "rube goldberg" to me, but it has worked for many years.
That is, until we moved the SQL2000 server to a seperate machine to improve program responsiveness.
Now when the trigger is fired and the log entry is made, the EntryWritten message is broadcast into the windows environment of the dedicated SQL server where there are no applications listening for it. Meanwhile, the applications continue to run with unrefreshed data on the (now) dedicated RDP server from where the EntryWritten messages cannot be "heard".
So my question really comes down to this...
In an environment where the SQL server and the RDP server are two seperate machines, what is the best method for coordinating multi-user screen refreshes across seperate applications running in distinct RDP Client sessions?
Thanks in advance for any assistance.
Peace,
Colt Taylor
Computer Golf Sofware
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Oct 25, 2006
I have developed two programs that operates against the same database. One of the program is just a display program that displayes the data put into the other administation program where you put in the data to be displayed (an administration program).
Every time I access the db from the administration program, the display program stops and throws connection pool errors and other database errors. For me, it looks like it doesīt do multi-access to a database.
I have tried putting user instance to off in both programs, but this didnīt help.
Connection string also points to same file database.
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Sep 11, 2007
Please help....
I have designed an application that uses sql server 2005 express database. This application was intended to be installed and used on a local desktop machine. However, now this application needs to be also installed on several computers and still needs to use only 1 database. Part of the database saves local user settings, so what I have done thus far is use two connection strings: one for local database (because the application may be used as origionally intended) and one for remote database that everyone should be able to connect to.
When I remotely connect to the database, it works fine. However, it seems to be locked so when I chose the same database for another user I get the error message "This File Is In Use." I need to know how to unlock it and make it usable for several users at the same time.
Thank you for your help! Please let me know if you need more information or if something is unclear in my description.
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Feb 6, 2004
Hi,
I am developing reporting application (access project) which will be used in multi user environment.
Here is what I have:
1 SQLServer database for many users
Each report will be based on:
stored procedure which creates a table filtered for specific dates predefined views will use the newly generated table to show results to the client. However, if more than 1 person runs reports results will not be accurate if each person specified different dates because they will look at the same table and results will match only for a user who called the stored procedure last.
what can you recommend - how to report in multi user environment?
Many thanks
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Oct 4, 2007
Hi all,
I just want to know if SSCE 3.0/3.5 can cater for Multi-user instances? I have a desktop application that I want to allow multiple Windows-user accounts to access. basically I need a datastore that can be lightweight (which SSCE is) and support "User Instances" (like in SQL Server Express)
thanx!
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Apr 19, 2007
Hi!
In my database I have all business logic in stored procedures. For example there are procedures: ReadBike and UpdateBike. Bike is business object stored in 4 tables.
On my system work 100 employees and we have one problem with this. The stroy is;
1. User A reads data about Bike1
2. User B reads data about Bike1
3. User A updates data about Bike1 (user B have old data)
4. User B updates data about Bike1
So user B don't know about chnages made by user A. How to solve that ptroblem?
It's probably solved in ADO, but I want use business login in procedures.
Regards,
Walter
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Mar 27, 2008
I am new to SQL Server but have been using Access to provide Multi-User acces to a central data store. We are evaluating the replacement of Access with SQL Server. With Access we don't need any special installation; I believe that the Jet Database Engine installed locally on each user's PC allows them to work with this in a disconnected manner; we use ADO.net 2.0 with VB.net 2005.
If each user has a locally installed SQL Server Express can they all attach to a database that resides on a shared network location?
In another post on the Forum I see the following regarding multi-user access:
Our application You will need to pick a central computer that everyone will be using the access the data and attach the file to the parent instance of SQL Express on that comuter, giving it a name that you can use to access it. Then you will need to modify your connection string to connect to the named database on the central server...
Can multiple locally installed SQL Server Express instances attach to a single data store that resides on a shared network location?
If not, what permissions do I need to create a parent instance of SQL Server Express?
Thank you for helping me understand how to implement our solution.
JudiR
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Dec 12, 2006
Can a SQL Server 2005 Compact Edition database file be deployed on a file share and be accessed by multiple (5-10) concurrent users? This is a current scenario being implemented at several sites using MS Access databases.
Each client would have the SQLce engine installed on it and would only access the database via a managed C# application.
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Mar 22, 2012
I am trying to place a database offline.
When I right in Microsoft SQL Server Management Studio on the database > Take Offline
Set offline failed for Database 'OperationsManagerAC'.
Transaction (Process ID 56) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction. ALTER DATABASE statement failed. (Microsoft SQL Server, Error: 1205)
So I am trying with some queries to pass the database from Single user to multi user but it fails
USE [master]
GO
ALTER DATABASE OperationsManagerAC SET MULTI_USER GO
Msg 1205, Level 13, State 68, Line 1</p><p>Transaction (Process ID 52) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.
Msg 5069, Level 16, State 1, Line 1
ALTER DATABASE statement failed.
I tried also
alter DATABASE OperationsManagerAC SET OFFLINE WITH ROLLBACK IMMEDIATE
IT FAILS AS WELL... with the same error... how to run the SQL Statements without using
How to proceed next?
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Jan 20, 2007
I was wondering if you guys might give me some advice on how best to handle a particular scenario i'm struggling with.
I have a client that basically wants web-based-update access to their sql server database. Specifically, for a group of users to be able to access a page where they select a record for editing. the caveat is that no two users should be able to pull up the same record at the same time. Originally I would have thought there was some easier record-locking-mechanism I could exploit within sql server or ado.net itself, but I haven't been able to come up with anything.. so this is my current approach:
The page they use starts-out with basically a blank form. there are custom-built paging controls at the bottom of the screen. they click page-forward to begin and a stored procedure is ran to select a record and update a field on that record to indicate "in-process". when they finish editing the record - or page on to the next record without updating - another stored procedure is ran - updating/resetting the status field on the record appropriately.
The entire page is encapsulated within an ajax.net updatepanel.
The entire page has caching disabled. This works well in conjunction with the first page being blank. if they get out of the app and try to get back in by clicking the back button - all they can do is get to the first (blank) page.
A piece of javascript window.onunload clicks a button on the page that releases the record they currently have selected in the event of a re-direct, clicking back, etc.. it appears to work with everything except a window close. in that case, i have a stored procedure running periodically on the server that checks how long a record has been selected - and if it exceeds the time indicated - resets the record as to allow it to be re-selected later.
In the event of session timeout, they are redirected to another page that tells them their session has timed-out (and since the window.onunload fires - it takes care of releasing the record if they have one on the screen).
The concept seemed to be working well until I started multi-user testing. Now it seems as if two users time it perfectly - they are actually able to both select the same record. it happens pretty rarely, but it does seem to happen. I'm guessing this has to do with how my stored procedure is structured - possibly allowing a tiny-enough window between the record being selected for editing - and the update running to actually status the record as in-process (2 separate sql statements within the one stored procedure).
I believe I also have a found a second quirk in my approach where something is causing the window.onunload event to fire twice in some strange situations.. but that's more annoying/confusing from a logging standpoint than anything..
I've read where people say to ensure you dont update a record that's already been updated - that you should compare the fields before you actually perform the update and ensure they haven't changed since you selected it.. but to me that doesn't solve anything.. if two people select the same record and both spend time working on it - the person that tries to update last has just wasted their time.
I've also toyed with the idea of maintaining a separate table in the database to hold the keys to the currently selected records and use that to keep multiple people from selecting the same record - but honestly i dont know if that approach is any better than what i'm doing now.
anyway, I was just curious if you guys had any advice in regards to how you'd handle a request like this.. or if you see any obvious problems/fixes with my current approach..
I would greatly appreciate any info you could provide-
thanks-
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Mar 4, 2015
I have tried everything I found on Google, but nothing seems to be working. Already Ran alter command set multi_user, but getting an error.
"Msg 5064, Level 16, State 1, Line 1
Changes to the state or options of database cannot be made at this time. The database is in single-user mode, and a user is currently connected to it.
Msg 5069, Level 16, State 1, Line 1..ALTER DATABASE statement failed."
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Apr 22, 2006
Good Day,
I have an application that is being developed on Visual Studio 2005 (VB) and SQL Express. The application is set up to use the SQL Express on the development computer, and if an Internet or CD install is built, it installs SQL Express as expected. The question is, when it is time to deploy and put the SQL Express database on the 2003 server, how should the install on the server be done and how should we set the database path to the server?
Thanks,
Dave
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Apr 28, 2008
I have a report that includes two multi-valued parameters.
In the Default Values section, I choose 'from query' and select dataset and value field.
In the Available Values section, I choose 'from query' select the same dataset and value field, and in the label field I select the relevant label field.
When I run the report my multi-valued parameters look like I selected the option 'select all' (all options are selected).
How can I keep the multi-valued parameters cleared from selections until the user select his choice? Thanks in advance.
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Oct 30, 2007
Hi guys,
I've been developing desktop client-server and web apps and have used Access and SQL Server Standard most of the time.
I'm looking into using SQL CE, and had a few questions that I can't seem to get a clear picture on:
- The documentation for CE says that it supports 256 simultaneous connections and offers the Isolation levels, Transactions, Locking, etc with a 4GB DB. But most people say that CE is strictly a single-user DB and should not be used as a DB Server.
Could CE be extended for use as a multi-user DB Server by creating a custom server such as a .NET Remoting Server hosted through a Windows Service (or any other custom host) on a machine whereby the CE DB would run in-process with this server on the machine which would then be accessed by multiple users from multiple machines??
Clients PCs -> Server PC hosting Remoting Service -> ADO.NET -> SQL CE
- and further more can we use Enterprise Services (Serviced Components) to connect to SQL CE and further extend this model to offer a pure high-quality DB Server?
Clients PCs -> Server PC hosting Remoting Service -> Enterprise Services -> ADO.NET -> SQL CE
Seems quite doable to me, but I may be wrong..please let me know either ways
Thanks,
CP
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Jul 10, 2007
Okay, I've read massive topics on ClickOnce, and embedded database applications, etc, etc.
I need a handful of good suggestions how I can create a deployment package, to get my sql express database onto a SQL Express server.
The database will need to be multi-user, because I am also developing a WinForms application to connect to the SQL Express database.
I'm thinking I need to use some automated scripting features, to generate scripts for the database once I am done (unless you have a better suggestion).
After that, I need to know what to do with those scripts, and how can I create a setup / deployment packages to run those scripts against a SQL Express server.
The other alterntative obviously is to copy my sql express database, and run an attach command. This will work the first time, only because this will have been the first deployment of this database.
Please keep in mind when answering this question, that I will not be embedding the database, and as far as I understand ClickOnce is a feature for use with embedded databases or user instance databases (not sure).
Daniel Crane
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Sep 23, 2014
Disaster Recovery Options based on the following criteria.
--Currently running SQL 2012 standard edition
--We have 18000 databases (same schema across databases)- majority of databases are less than 2gb-- across 64 instances approximately
--Recovery needs to happen within 1 hour (Not sure that this is realistic
-- We are building a new data center and building dr from the ground up.
What I have looked into is:
1. Transactional Replication: Too Much Data Not viable
2. AlwaysOn Availability Groups (Need enterprise) Again too many databases and would have to upgrade all instances
3. Log Shipping is a viable option and the only one I can come up with that would work right now. Might be a management nightmare but with this many databases probably all options with be a nightmare.
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Aug 17, 2015
More often than not, I typically don't touch DTC on clusters anymore; however on a project where the vendor states that it's required. So a couple things here.
1) Do you really need DTC per instance or one for all?
2) Should DTC be in its own resource group or within the instance's group?
2a) If in it's own resource group, how do you tie an instance to an outside resource group? tmMappingSet right?
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Feb 4, 2008
the stored procedure don't delete all the records
need help
Code Snippet
DECLARE @empid varchar(500)
set @empid ='55329429,58830803,309128726,55696314'
DELETE FROM [Table_1]
WHERE charindex(','+CONVERT(varchar,[empid])+',',','+@empid+',') > 0
UPDATE [empList]
SET StartDate = CONVERT(DATETIME, '1900-01-01 00:00:00', 102), val_ok = 0
WHERE charindex(','+CONVERT(varchar,[empid])+',',','+@empid+',') > 0
UPDATE [empList]
SET StartDate = CONVERT(DATETIME, '1900-01-01 00:00:00', 102), val_ok = 0
WHERE charindex(','+CONVERT(varchar,[empid])+',',','+@empid+',') > 0
TNX
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Jul 20, 2005
Hello,I am trying to construct a query across 5 tables but primarily 3tables. Plan, Provider, ProviderLocation are the three primary tablesthe other tables are lookup tables for values the other tables.PlanID is the primary in Plan andPlanProviderProviderLocationLookups---------------------------------------------PlanIDProviderIDProviderIDLookupTypePlanNamePlanIDProviderStatusLookupKeyRegionIDLastName...LookupValue....FirstName...Given a PlanID I want all the Providers with a ProviderStatus = 0I can get the query to work just fine if there are records but what Iwant is if there are no records then I at least want one record withthe Plan information. Here is a sample of the Query:SELECT pln.PlanName, pln.PlanID, l3.LookupValue as Region,p.ProviderID, p.SSNEIN, pl.DisplayLocationOnPCP,pl.NoDisplayDate, pl.ProviderStatus, pl.InvalidDate,l1.LookupValue as ReasonMain, l2.LookupValue as ReasonSub,pl.InvalidDataFROM Plans plnINNER JOIN Lookups l3 ON l3.LookupType = 'REGN'AND pln.RegionID = l3.Lookupkeyleft outer JOIN Provider p ON pln.PlanID = p.PlanIDleft outer JOIN ProviderLocation pl ON p.ProviderID = pl.ProviderIDleft outer JOIN Lookups l1 ON l1.LookupType = 'PLRM'AND pl.ReasonMain = l1.LookupKeyleft outer JOIN Lookups l2 ON l2.LookupType = 'PLX1'AND pl.ReasonSub = l2.LookupkeyWHERE pln.PlanID = '123456789' AND pl.ProviderStatus = 0ORDER BY p.PlanID, p.ProviderID, pl.SiteLocationNumI know the problew the ProviderStatus on the Where clause is keepingany records from being returned but I'm not good enough at this toanother select.Can anybody give me some suggestions?ThanksDavid
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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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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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