Definition
Plain language
A guarantee that once you've been shown a piece of data, the system will never later hand you an older version of it.
As stated in the literature
A session-consistency property ensuring a client's successive reads never observe state older than a previously observed value; one of the correctness specifications verified for distributed key-value stores in the Inductive-Deductive Synthesis work, alongside causal consistency.
Why it matters: It prevents the confusing experience of data appearing to move backward in time, keeping a user's view of a system consistent.
For example, once a shopping app shows you an item is out of stock, it won't later flip back to showing it as in stock from stale data.
Heard on the show
“They cover the correctness-critical core of a distributed key-value store — read your writes, monotonic reads and writes, causal consistency, and a couple of variants.”Episode 075 — Growing Code and Proof Together: Verified Systems in Ten Hours Instead of a Year