One efficient means of solving the problem of unique primary keys is to assign each user of the database a pool of primary key values that can be used as the need arises. For example, you can assign each sales representative 100 new identification values. Each sales representative can freely assign values to new customers from his or her own pool.
Following is an overview of how to implement a primary key pool.
Add a new table to the consolidated database and to each remote database to hold the new primary key pool. Apart from a column for the unique value in the consolidated database, these tables should contain a column for a user name, to identify who has been given the right to assign the value.
In the consolidated database, write a stored procedure to ensure that each user is assigned enough new identification values. Assign more new values to remote users who insert many new entries or who synchronize infrequently.
Write a download_cursor script to select the new values assigned to each user and download them to the remote database. See Implementing timestamp-based downloads.
Modify the application that uses the remote database so that when a user inserts a new row, the application uses one of the values from the pool. The application must then delete that value from the pool so it is not used a second time.
Write an upload_delete script to upload the deleted keys. The MobiLink server then deletes rows from the consolidated pool of values that a user has deleted from his personal value pool in the remote database.
Write an end_upload script to call the stored procedure that maintains the pool of values. Doing so has the effect of adding more values to the user's pool to replace those deleted during upload.
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