> Do transactional emails get sent out again? Do upstream services record the playback as duplicate events? How are transactions handled? The narrow problem he

> Do transactional emails get sent out again? Do upstream services record the playback as duplicate events? How are transactions handled? The narrow problem here is that Event Sourcing is temporal, but not bitemporal. Or rather, the different kinds of temporality are frequently muddled. Event streaming in the Akidau/Google style is bitemporal, but mostly accidentally, as a side effect of distinguishing "event time" (fact time) and "processing time" (transaction time / belief time). (Snodgrass later proposed tritemporal models, including a timeline for when a fact-belief was viewed, which I find both brilliant and slightly terrifying). The problems of evolving data models, which is the third-order problem, is often hardest when you put a log or stream at the centre of your design. Databases using SQL, for example, struggle with first-order (current state) and second-order (historical state) evolution. But they do much better on third-order evolution, since DDL is built into every relational database.