Event Sourcing: The Interview Version

1. The Definition, and the Distinction That Scores

Event sourcing means the source of truth is an append-only log of events, not a table of current state. Append-only means you only add new records to the end. You never update or delete one that is already there.

Here is the contrast. A conventional account row stores balance: 70. An event-sourced account stores Opened(0), Deposited(100), Withdrew(30). The balance 70 is derived by replaying those events in order. State becomes a cache. History becomes the truth.

Now draw the line that most candidates blur