ACC1x: Multiple Users Adding Fields Causes Cross-Linking

• Microsoft Access version 1.0

SYMPTOMS

Incorrect data appears in tables when multiple users load and modify the same database within minutes of each other.

The steps below describe a typical scenario in which this problem occurs:

1. User1 opens a table in a database.

2. User2 opens the same database and makes a change to the design of the table User1 has open.

3. Less than one minute later, User1 makes a change to the design of the same table.

• Data from one field in the table may be displayed in a new field.
• Data in a new or changed field may be displayed in a second field.
• Attempting to copy the table containing new or changed fields generates an error message.

CAUSE

This problem, called cross-linking, occurs because information about tables in a database is read from the system tables and is cached into memory by Microsoft Access when a user opens a database. The information in a user's cache may become obsolete if another person has just made a change and Microsoft Access does not read the new information before the first user makes changes. For example, in the situation above, User1 has cached the information for the table, User2 makes a change, and then User1 makes a change before the system tables are reread. If this occurs, the table can become corrupted.

It is not necessary for both users to open or change the same table for corruption to occur. The information for the table opened by User1 may be on the same page in the system table as the information for the table modified by User2. If that page is cached by Microsoft Access, table corruption may occur.

RESOLUTION

Information in the cache for tables not currently in use is discarded on a regular basis, so problems do not occur unless changes are made before Microsoft Access has had an opportunity to empty the cache. To ensure that information in the cache is emptied, wait a minimum of one to two minutes before opening the table in Design view.

If the database is corrupted, compacting the affected database usually corrects the problem. To do this, close all databases and choose Compact Database from the File menu.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Access version 1.0. This problem no longer occurs in Microsoft Access version 1.1.