Patient List Reminders and Patient Export Reminders are each processed in a single batch by Reporting - Reminders - Send All. On successful completion of the list/export they are each batch updated in a single transaction. This ensures that if the update fails, the original list/export can be discarded and retried.
At present, there is no limit on how many reminders can be processed in this way. In practice, large numbers may cause transaction timeouts.
On one database, updating 20000 List reminders timed out and rolled back. .
To avoid this, List and Export reminders should not attempt to process all available reminders, but should terminate after processing a fixed number (e.g. 1000). A message should be displayed to indicate this.