> For the complete documentation index, see [llms.txt](https://wiki.dmmax.me/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://wiki.dmmax.me/distributed-systems/delivery-guarantee.md).

# Delivery guarantee

## At most once

This guarantee ensures that a message is delivered at most once, but there is a possibility that it may not be delivered at all.

## At least once

This guarantee ensures that a message is delivered at least once, but it may be delivered multiple times.

## Exactly once

This guarantee ensures that a message is delivered exactly once, and not more or less.

## Links

* [Article by Tyler Treat: You Cannot Have Exactly-Once Delivery](https://bravenewgeek.com/you-cannot-have-exactly-once-delivery/)