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I'm working on upsizing a suite of MS Access backend databases to SQL Server. I've scripted the SQL to create the table schemas in SQL Server. Now I am trying to populate the tables. Most of the tables have autonumber primary keys. Here's my general approach:

For each TblName in LinkedTableNames
    'Create linked table "temp_From" that links to the existing mdb'
    'Create linked table "temp_To" that links to the new SQL server table
    ExecutePassThru "SET IDENTITY_INSERT " & TblName & " ON"
    db.Execute "INSERT INTO temp_To SELECT * FROM temp_From", dbFailOnError
    ExecutePassThru "SET IDENTITY_INSERT " & TblName & " OFF"
Next TblName

The first insert happens immediately. Subsequent insert attempts fail with the error: "Cannot insert explicit value for identity column in table 'TblName' when IDENTITY_INSERT is set to OFF."

I added a Resume statement for that specific error and also a timer. It turns out that the error continues for exactly 600 seconds (ten minutes) and then the insert proceeds successfully.

Does MS Access automatically refresh its ODBC sessions every 10 minutes? Is there a way to force that to happen faster? Am I missing something obvious?

Background info for those who will immediately want to say "Use the Upsizing Wizard":
I'm not using the built-in upsizing wizard because I need to be able to script the whole operation from start to finish. The goal is to get this running in a test environment before executing the switch at the client location.

mwolfe02
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3 Answers3

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I found an answer to my first question. The ten minutes is a setting buried in the registry under the Jet engine key:

'Jet WinXP/ Win7 32-bit:'
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Jet\4.0\Engines\ODBC\ConnectionTimeout

'Jet Win7 64-bit:'
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Jet\4.0\Engines\ODBC\ConnectionTimeout

'ACE WinXP/ Win7 32-bit:'
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Access Connectivity Engine\Engines\ODBC\ConnectionTimeout

'ACE Win7 64-bit:'
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\MicrosoftAccess Connectivity Engine\Engines\ODBC\ConnectionTimeout

It is documented here for ACE:

ConnectionTimeout: The number of seconds a cached connection can remain idle before timing out. The default is 600 (values are of type REG_DWORD).

This key was set to the default of 600. That's 600 seconds or 10 minutes. I reduced that to ten seconds and the code sped up accordingly.

This is by no means the full solution, because setting the default that low is sure to cause issues elsewhere. In fact, Tony Toews once recommended that the default might better be increased when using DSN-less connections.

I'm still hoping to find an answer to the second part of my question, namely, is there a way to force the refresh to happen faster.

UPDATE: The reason this is even necessary is that the linked tables use a different session than ADO pass-through queries. I ran a test using SQL Profiler. Here are some brief results:

TextData                               SPID
-------------------------------------------
SET IDENTITY_INSERT dbo.TblName ON       50
SET IDENTITY_INSERT "dbo"."TblName" ON   49
exec sp_executesql N'INSERT INTO "d...   49
SET IDENTITY_INSERT dbo.TblName OFF      50
SET IDENTITY_INSERT dbo.NextTbl ON       50
SET IDENTITY_INSERT "dbo"."NextTbl" ON   49
exec sp_executesql N'INSERT INTO "d...   49

What's going on here is that my ADO commands are running in a different session (#49) than my linked tables (#50). Access sees that I'm setting the value for an identity column so it helpfully sets IDENTITY_INSERT ON for that table. However, it never sets IDENTITY_INSERT OFF. I turn it off manually, but that's happening in a different session.

This explains why setting the ODBC session timeout low works. It's just an ugly workaround for the fact that Access never turns off IDENTITY_INSERT on a table once it turns it on. Since IDENTITY_INSERT is sessions-specific, creating a new session is like hitting the reset button on IDENTITY_INSERT. Access can then turn it on for the next table and the setting will take effect because it's a brand new session.

mwolfe02
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Two thoughts, though not sure either will be useful because this is unfamiliar territory for me.

"Does MS Access automatically refresh its ODBC sessions every 10 minutes? Is there a way to force that to happen faster? Am I missing something obvious?"

In the Access 2003 Options dialog, on the Advanced tab, there is a setting for "ODBC refresh interval" and also settings for retries. Does adjusting those help ... or have any effect at all?

I wonder if you could avoid this problem by creating the SQL Server columns as plain numbers rather than autonumber, INSERT your data, then ALTER TABLE ... ALTER COLUMN to change them after the data has been inserted.

Access won't let me convert a numeric column to an autonumber if the table contains data, but ISTR SQL Server is more flexible on that score.

HansUp
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    +1 Good ideas both. I didn't try the first suggestion because I found the setting I was after buried in the registry (I'll add that as a separate answer). The second approach is straightforward using the SQL Server Mgmt Studio, but that hides the inherent inefficiency required. It actually involves copying all of the records to a temporary table (making use of SET IDENTITY_INSERT ON/OFF), dropping the original table, and renaming the temp table to the original. One of my tables has 2 million+ records, so I wanted to avoid that inefficiency. – mwolfe02 Aug 08 '11 at 20:56
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I found a convenient whereas not so beautiful solution to export many access tables to sql server and avoid the identity_insert problem:

  1. I open a local table-recordset which lists all tables to be exported and I loop through the records (each table). In each loop I...

  2. create an access application object

  3. use the transfer database method on application object

  4. terminate / quit the application object and loop again

Here is the sample code:

Public Sub exporttables()
Dim rst As Recordset
Dim access_object

'First create a local access table which lists all tables to be exported'
Set rst = CurrentDb.OpenRecordset("Select txt_tbl from ####your_table_of_tables####")

 With rst
 While Not .EOF
    'generate a new object to avoid identity insert problem'
    Set access_object = CreateObject("Access.Application")
    'with access object open the database which holds the tables to be exported'
    access_object.OpenCurrentDatabase "####C:\yoursourceaccessdb####.accdb"
    access_object.DoCmd.TransferDatabase acExport, "ODBC Database", "ODBC;DSN=####your connection string to target SQL DB;", acTable, .Fields("txt_tbl"), .Fields("txt_tbl"), False, False
    Debug.Print .Fields("txt_tbl") & " exported"
    access_object.CloseCurrentDatabase
    access_object.Application.Quit
    Set access_object = Nothing
    .MoveNext
Wend
End With

Set rst = Nothing
End Sub
Florian Weihs
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