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Q155232: BUG: Access Driver Ignores Pagetimeout in Datasources

Article: Q155232
Product(s): Open Database Connectivity (ODBC)
Version(s): WINDOWS:3.40
Operating System(s): 
Keyword(s): 
Last Modified: 11-DEC-1999

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The information in this article applies to:

- Microsoft Open Database Connectivity, version 3.40 
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SYMPTOMS
========

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

WORKAROUND
----------

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.

To work around this problem:

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 then 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.

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

In addition, the Access ODBC driver supports a distinct Pagetimeout value for
each ODBC datasource. This can be specified in Advanced options when you
configure a data source manually in the ODBC Administrator. The value specified
in the datasource is ignored. The ODBC driver always uses the Pagetimeout value
from the registry location mentioned above. If the Jet key does not exist or
does not include a specified Pagetimeout value, the driver always uses the Jet
default of 5 seconds.

Additional query words: odbc 3.40.2829

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbODBCSearch
Version           : WINDOWS:3.40
Issue type        : kbbug
Solution Type     : kbpending

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