Writing archive

Two requests read the same row, both change it, and the second save quietly erases the first. A version number turns that silent bug into a conflict you can catch. Here is how optimistic locking works.

Most API errors are written for a human reading logs, not for the program that has to react. Here is what most APIs do, what the standard says, and the small set of rules that actually make errors useful.

You save to the database and publish an event to a queue. These are two writes, and one can fail. The outbox pattern makes them one. Here is how.

When two systems edit the same record, last-write-wins is the easy answer. It also throws away data on purpose. Here is when that is fine, and when it is a trap.

When you really delete a row, other systems can never learn that it is gone. A tombstone is a delete you can see. Here is why it matters and how to use one.