DOCUMENT:Q178942  17-JUL-2001  [visualc]
TITLE   :HOWTO: Performance Tuning the Jet Engine Per Instance in MFC
PRODUCT :Microsoft C Compiler
PROD/VER:WINNT:5.0,6.0
OPER/SYS:
KEYWORDS:kbDAOsearch kbJET kbMFC kbVC500 kbVC600

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The information in this article applies to:

 - The Microsoft Foundation Classes (MFC) 
 - Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
 - Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
 - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SUMMARY
=======

MFC does not document or directly expose any methods to manipulate the
performance parameters of the Jet Database (DB) engine. However, if you are
using DAO 3.5, you can gain access to the DB engine from within an MFC
application and alter the performance characteristics just for the instance of
the Jet engine your application is using. This method allows the user to
programatically set performance characteristics, which will apply only to the
specific application. For example, the MaxBufferSize could be set during program
startup.

MORE INFORMATION
================

To gain access to the functions that allow manipulation of Jet, you must first
get access to the DB engine. The undocumented function AfxDaoGetEngine() returns
a pointer to the current instance of the DB engine. The function is found in
Daocore.cpp:

      DAODBEngine* AFXAPI AfxDaoGetEngine()
      {
        // Return DAODBEngine object for direct access
        return AfxGetDaoState()->m_pDAODBEngine;
      }

The following line of code returns a pointer to the DB engine. No special header
files are required:

      DAODBEngine* m_pDAODBEngine = AfxDaoGetEngine();

Once you have a pointer to the DB engine, the DAO SDK function SetOption() can be
used to set performance parameters. These parameters only affect the specific
instance of the engine for your application. They do not affect the default Jet
performance parameters stored in the registry. The following code examples show
how to change some of the specific parameters:

      // Change the MaxBufferSize to 128. When doing thousands of
      // inserts, this will restrict memory growth.
      COleVariant  vBufferSize((long)128, VT_I4);
      m_pDAODBEngine->SetOption( dbMaxBufferSize, vBufferSize );

      // Reduce the time to defer asynchronous flushes on a
      // database opened for exclusive use.
      COleVariant  vExclusiveAsyncDelay((long)10, VT_I4);
      m_pDAODBEngine->SetOption(dbExclusiveAsyncDelay,vExclusiveAsyncDelay);

      // Reduce the time to defer asynchronous flushes on a
      // database opened for shared use.
      COleVariant vSharedAsyncDelay((long)15, VT_I4);
      m_pDAODBEngine->SetOption(dbSharedAsyncDelay, vSharedAsyncDelay);

NOTE: It is necessary to cast the first parameter in the constructor for the
COleVariant in order to avoid the "ambiguous call to overloaded function" error
at compile time.

The following values and their defaults can be changed:

   
   +--------------------------------+
   | PageTimeout             | 5000 | 
   +--------------------------------+
   | SharedAsyncDelay        | 100  | 
   +--------------------------------+
   | ExclusiveAsyncDelay     | 2000 | 
   +--------------------------------+
   | LockRetry               | 20   | 
   +--------------------------------+
   | UserCommitSync          | Yes  | 
   +--------------------------------+
   | ImplicitCommitSync      | NO   | 
   +--------------------------------+
   | MaxBufferSize           | 0    | 
   +--------------------------------+
   | MaxLocksPerFile         | 9500 | 
   +--------------------------------+
   | LockDelay               | 100  | 
   +--------------------------------+
   | RecycleLVs              | 0    | 
   +--------------------------------+
   | FlushTransactionTimeout | 500  | 
   +--------------------------------+

References
----------

Note: The best source for additional information on these settings is the Access
97 Help Files. Search for the topic:

   Initializing the Microsoft Jet 3.5 Database Engine Driver

Additional query words: defaults settings registry

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Keywords          : kbDAOsearch kbJET kbMFC kbVC500 kbVC600 
Technology        : kbVCsearch kbAudDeveloper kbMFC kbVC500 kbVC600 kbVC32bitSearch kbVC500Search
Version           : WINNT:5.0,6.0
Issue type        : kbhowto

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