Vector Clocks

1. The Pattern

Version each key with a small table containing one counter per writer, and increment the writer's counter after every write. You can then compare any two versions. If every counter in one version is greater than or equal to the matching counter in another, it knew about and supersedes the other version. If each version is ahead somewhere, the writes were concurrent, so the system detects a true conflict instead of silently losing data.

The quorum lesson ended with two devices updating one cart concurrently