BUG: Access Driver Ignores Pagetimeout in Datasources

• Microsoft Open Database Connectivity, version 3.40

SYMPTOMS

The Access ODBC driver ignores the Pagetimeout parameter specified in ODBC datasources.

WORKAROUND

To work around this problem:

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

1. Run Registry Editor (REGEDT32.EXE).

2. From the HKEY_LOCAL_MACHINE subtree, go to the following key:

         \SOFTWARE\Microsoft\Jet\3.0\Engines
   

3. From the Edit menu, select Add Key and enter the following key: Jet

4. Select the Jet key.

5. From the Edit menu, select Add Value.

6. Add the following:

         Value: PageTimeout
         Data Type: REG_DWORD
         Data: <Decimal value in milliseconds>
   

   NOTE: If this value is set too low, performance may degrade due to Jet increasing its reading of the mdb file. Do not set the value lower than the Jet 2.0 default of 0.5 second. The PageTimeout parameter is expressed in 100 millisecond units. So, a value of 5 stands for 500 milliseconds or .5 seconds.

7. Click OK.

8. Quit Registry Editor.

9. Shut down and restart Windows NT.

STATUS

Microsoft has confirmed this to be a problem in the ODBC Access 3.40.2829 Driver. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The Access ODBC driver is built on the Jet Database Engine. Jet buffers the pages read from a mdb file. The interval at which Jet reads pages from the mdb file to refresh the buffer is controlled by a Pagetimeout parameter. Jet does not refresh its internal buffer from the mdb file until the Pagetimeout interval has expired (even if you issue a Select against the table whose data is in those pages). If you do Select Jet provides the information from the buffer. It does not actually read pages in from the mdb file until the Pagetimeout interval has expired.

If multiple instances of Jet (such as separate connections through the Access driver or separate instances of Access) are working with the same mdb file, updates made by one task is not visible to a second task until after the second task's Pagetimeout interval has expired. For example, if the second task s Pagetimeout interval is set to 20 seconds, the updates made by the first task is not visible to the second task for 20 seconds.

In Jet 2.0, which is the version used in the ODBC Desktop Drivers version 2.0, the Jet Pagetimeout interval defaults to 0.5 second. In Jet 3.0, which is the version used in the ODBC Desktop Drivers 3.0, the default has been raised to 5 seconds. Therefore, users have noticed that updates, inserts, and deletes made in one Jet task (either the ODBC Access driver or Access itself) does not appear in another Jet task for 5 seconds.

The Pagetimeout interval can be specified in two places. The default for all instances of Jet on a computer is stored in the following Windows NT Registry subkey:

   HKEY_LOCAL_MACHINE\Software\Microsoft\Jet\3.0\Engines\Jet