Transaction

The source stock example rejects a watched stale queue after a rival changes stock from 2 to 1; the marker remains absent. A new watched attempt reads 1 and commits 0 with the marker. MULTI/EXEC alone cannot repair an earlier stale read.

WATCH protects Redis read-modify-write decisions

MULTI/EXEC prevents another client’s commands from interleaving while the queued commands execute. That alone does not protect a value read earlier in the application. If two buyers read the same stock count and later write their own calculated value, wrapping each SET in a transaction can still lose an update. ...