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MS Access Limit Number of Simultaneous Users to 10

Posted on 2014-11-18
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Last Modified: 2014-11-22
Hi,
In a multi - User environment,  I need to limit the number of simultaneous users to 10.
There are multiple back - ends on the server linked to each front - end on each users desktop.
A permanent open connection ( via linked tables to each of the back-ends) is created when the first form, frmDashboard opens.
(fsubDashboard1,  fsubDashboard2,  etc has tblLink1,  tblLink2 etc as the record source).
How can I prevent the 11th user from login - on,  seeing that only 10 users should be logged-on simultaneously.
Your assistance is greatly appreciated.
Kind Regards,
Mohamed
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Question by:Mohamed Singh
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Accepted Solution

by:
Jim Dettman (Microsoft MVP/ EE MVE) earned 500 total points
ID: 40449861
You could use a commercial product such as:

http://www.peterssoftware.com/ka.htm

or build something in yourself using the ideas here:

http://www.experts-exchange.com/Database/MS_Access/A_5328-Resource-locking-in-your-applications.html

 Using this, you would create one "resource lock" for each user as they started up the app.  It would then be a simple matter to check the current number of locks and stop them if the limit was exceeded.

Jim.
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Expert Comment

by:James Elliott
ID: 40449869
There's probably any easier way of doing this, but you could use a logon trigger to write to a table. You could integrate some logic to rollback the 'transaction' if the server already has 10 active entries in your table.

http://technet.microsoft.com/en-us/library/bb153915(v=sql.105).aspx
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Expert Comment

by:Dale Fye (Access MVP)
ID: 40449903
Can I ask why you want to limit concurrent access to 10 users?  Are you seeing a significant degradation in performance when you reach 10 users?

In addition to logging users into your application, you must also log them out of your application.

Occasionally, users will fail to log out of your application neatly, where neatly is defined as closing the application so that their logon will be released.  Sometimes, they will just close Access or their system will lock up and they will have to use the task manager to close Access (hopefully your error handler will prevent this necessity).  So you must provide a way to reset your logins.
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Author Comment

by:Mohamed Singh
ID: 40449935
Hi,
Thank You Jim Dettman and James Elliott for responding.
I actually used a procedure similar to James Elloitt's suggestion, and then granted the database administrator the access to uncheck tblUser.LoggedIn via frmUsers to provide for the unforseen instances where a user still has a record as being logged-on.
But, perhaps Jim Dettman's resource locking is a better solution.
Nevertheless, is there no method of interrogating the database engine ?
Kind Regards,
Mohamed
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Author Comment

by:Mohamed Singh
ID: 40449944
Actually I have Keyed Access as well, just didn't get around to using it.
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LVL 57
ID: 40449949
<<Nevertheless, is there no method of interrogating the database engine ?>>

 No.  You need to store the number of concurrent users in some way, either in a table, as a lock on a file, in a file, etc.

There's nothing built into JET/ACE that allows a limit on the number of users.

Jim.
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Author Comment

by:Mohamed Singh
ID: 40449952
Hi Dale Fee,
I'm guarding against degradation and associated problems by limiting the number of simultaneous users.
Thank You for participating.
Kind Regards,
Mohamed
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Author Comment

by:Mohamed Singh
ID: 40449978
Hi Jim,
Please see:
(But how reliable is this and it should provide for password protected backends )

Public Function CountUsersInDb(strDatabase As String)
        Dim cn As New ADODB.Connection
        Dim rs As New ADODB.Recordset
        Dim i As Integer

        On Error GoTo ExitHandler

        cn.Open "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & strDatabase & ";Persist Security Info=False"

        Set rs = cn.OpenSchema(adSchemaProviderSpecific, , "{947bb102-5d43-11d1-bdbf-00c04fb92675}")

        Do While Not rs.EOF
            i = i + 1
            rs.MoveNext
        Loop

ExitHandler:
        CountUsersInDb = i
        On Error Resume Next
        rs.close
        Set rs = Nothing
        cn.close
        Set cn = Nothing
    End Function
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Expert Comment

by:Dale Fye (Access MVP)
ID: 40449981
Mohamed,

I honestly don't remember where I found the code in the attached, but it identifies the computers (not the specific user) that are logged into a particular mdb or accdb file.  You might be able to incorporate it into your application to do the count for you.
WhosUsing.accdb
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Author Comment

by:Mohamed Singh
ID: 40449982
Also the function should be version independent.
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Author Comment

by:Mohamed Singh
ID: 40449989
Thank You Dale,
I will certainly look into it.
Kind Regards,
Mohamed
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Expert Comment

by:Dale Fye (Access MVP)
ID: 40449993
Mohamed,

I believe it is mostly the same as the code you posted just a minute before I posted
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Author Closing Comment

by:Mohamed Singh
ID: 40459084
Hi Jim,

I went with the resource locking as it has the potential to address many issues from one central point.

Kind Regards,
Mohamed
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