Actually, I am super excited about it! We haven't got a good tech conference that isn't just for Digital Agencies up here in Newcastle

I keep thinking every problem can be solved with Event Sourcing but then I question myself thinking... that can't be right.... but it is more often than not!

So the most important thing I think I get in an architecture that uses Event Sourcing is the flexibility to change the architecture piecemeal later when I find I've built the wrong thing!

how dyu tend to deal with schema changes in yr event-sourcing systems @agile_geek?

add new specs, all there is to it

or do you mean breaking change? don't make those 😄

In Java system I’m currently working on we are always accreting to API but my fellow team lead has been looking at Flink using Avro schema registry that clients use to get the appropriate schema.

uh @U09LZR36F i'm thinking of e.g. you introduce a new field to an entity, and you want to set the value of that field in historical records to some synthesis of other fields in that entity (or that entity joined to some other entity)

@U0524B4UW so a migration

?

yeah, something that you would do with a migration in a database

I’d deal with it in the local storage of the service reading the stream

dyu migrate your event history too ?

If you mean re-write the stream… no

i was thinking derive a new stream from the old stream maybe

Any local database wrapped in a service off the stream can decide what it wants to do

Yeah you could do

I would always keep the one source stream as a starting point with the ‘raw’ data eeven if it changed over time

The caveat would be don’t remove fields

just deprecate

> and you want to set the value of that field in historical records to some synthesis of other fields in that entity New events which update your models as an interim correction.

ah @U09LZR36F so would you introduce a schema-change event too, so that e.g. you can do a migration on a projected db... or just insist on backwards-compatible schema (no field deletions, no field type-changes, no constraint changes (e.g. PK change) making older events incompatible with later views)

That's one model I see recommended. I think accretion and event sourcing pair well.

Yeah, I understand.. but still that's a small number