O'Reilly logo
  • Zenifer Cheruveettil thinks this is interesting:

Consistency guarantees are typically bucketed into three main classes: at-most once processing, at-least once processing, and exactly-once processing.

From

Cover of Streaming Systems

Note

at-most once: data loss is possible
at-least once: no data loss, but possible duplicates
exactly-once: neither data loss, nor duplicates