Another weakness important to note is the difficulty of handling entities that can change over time. As a simple case, we have a
Processable model that asynchronously transitions from
processed. If an item is rolled up while pending but is then later processed, we need to go back and update the old count. If the processing time is short and predictable, we can get away with simply looking an additional period (or periods) back and recomputing the rollup. However if the processing time is unpredictable (e.g., anything requiring manual human action), we cannot do this solely at the DB level and would have to handle rollups with logic like "query every item that has updated since the last rollup period; handle items created after the rollup period normally; take items created before the rollup period and reconcile them back into existing rollups".