Active Record objects hold the database-derived state they loaded; they do not stay synchronized when another process changes the row. I built four small, reproducible experiments covering stale reads, lost updates, optimistic locking, and association-cache staleness, then looked at Rails’ abandoned Identity Map and what genuinely live objects would require.

https://syedaslam.com/posts/why-active-records-snapshot-semantics-are-a-trade-off/