Improving Performance

When you link or open external tables in a Microsoft Access database, you're accessing the data through an additional service layer (the installable ISAM). Because more overhead is required when maintaining a connection, transferring and translating data, and maintaining a external index in a foreign format, certain operations are significantly slower when you're using an external data source.

If your application only needs to read through records in an external table in a single pass, you can dramatically improve the performance of your application by using forward-only-type Recordset objects. There are a couple of disadvantages of using forward-only-type Recordset objects that you should be aware of. One is that your movement through the Recordset object is limitedyou can only move forward. The other is that the following DAO methods and properties are unavailable with forward-only-type Recordset objects:

 Bookmark property

 Clone method

 FindFirst method

 FindLast method

 FindNext method

 Move method (with any value other than 1)

 MoveFirst method

 MoveLast method

 MovePrevious method

 OpenRecordset method

Despite these disadvantages, using a forward-only-type Recordset object can significantly improve performance, especially when the external tables you are accessing are very large.

See Also   For more information on forward-only-type Recordset objects, see Chapter 9, "Working with Records and Fields," or search the Help index for "OpenRecordset method."

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