docs: eventstore (#1982)

* docs: eventstore

* Apply suggestions from code review

Co-authored-by: Florian Forster <florian@caos.ch>

Co-authored-by: Florian Forster <florian@caos.ch>

docs/docs/concepts/eventstore.md

@@ -0,0 +1,20 @@
+---
+title: Eventstore
+---
+
+ZITADEL is built on the [event sourcing pattern](architecture), where changes are stored as events in an eventstore.
+
+## What is an eventstore?
+
+Traditionally, data is stored in relations as a state
+
+- A request needs to know the relations to select valid data
+- If a relation changes, the requests need to change as well
+- That is valid for actual, as well as for historical data
+
+An Eventstore on the other hand stores events, meaning every change that happens to any piece of data relates to an event
+
+- Think of it as a ledger that gets new entries over time, accumulative
+- To request data, all you have to do is to sum the events as the summary reflects the actual state
+- To investigate past changes to your system, you just select the events from your time range of interest
+- That makes audit/analytics very powerful, due to the historical data available to build queries

docs/sidebars.js

@@ -144,6 +144,7 @@ module.exports = {
     'concepts/introduction',
     'concepts/architecture',
     'concepts/principles',
+    'concepts/eventstore',
   ],
   legal: [
     'legal/introduction',