> For the complete documentation index, see [llms.txt](https://note.levelcode.org/software-engineering-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://note.levelcode.org/software-engineering-notes/event-sourcing.md).

# Event-Sourcing

With our usual state-based system:

* CRUD operations executed on the DB table, which means we mutate the data as needed
* Current state can be seen directly at the DB

Meanwhile, with event-sourcing, we store extra data (every event) that happens, not storing only the last state.

* Create (append-only) and read operations only on DB tables
* To get the current state, the data must be processed (reduced) first
* Stored as event log, so no information loss
* We can replay and see the state at any point of time
* Events are immutable, allowing us to see evidence and how something happened (we can also see why something went wrong)


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