Consistent Prefix Reads
Summary: A guarantee that if a sequence of writes happens in a certain order, anyone reading those writes will see them appear in the same order.
Sources: chapter5
Last updated: 2026-04-15
Consistent prefix reads is a guarantee that maintains causality. If a sequence of writes happens in a certain order, then anyone reading those writes will see them appear in the same order (source: chapter5, p. 165).
This is a particular problem in partitioned (sharded) databases. If different partitions operate independently, there is no global ordering of writes, and an observer might see an answer before the question that prompted it if the partitions are replicated at different speeds (source: chapter5, p. 166).
Implementation
One solution is to ensure that any writes that are causally related to each other are written to the same partition. There are also algorithms that explicitly keep track of causal dependencies (source: chapter5, p. 167).