Optimistic Concurrency

2 articles

Software Engineering 21 Sep 2026 5 min read

Version Columns Turn Lost Updates into Detectable Conflicts

Version Columns Turn Lost Updates into Detectable Conflicts A read-modify-write flow can overwrite another committed change even when every individual database statement succeeds. Two clients read the same row, compute different replacements, then write in sequence. Without a condition tying each write to the state it read, the later write can silently erase the earlier one. A version column makes that dependency explicit. The client reads both data and version, then updates only if the stored version is still the one it observed. A changed version turns the race into a failed conditional update instead of a lost update.

Software Engineering Databases

Software Engineering 15 Sep 2026 7 min read

Version Columns Turn Lost Updates Into Explicit Conflicts

Two clients can read the same database row, derive different changes, and then write in sequence. If each update replaces values without checking the state that produced its decision, the later write can silently erase part or all of the earlier one. The database has serialized the statements, yet the application-level read-modify-write operation has still lost a concurrent change. A version column changes the admission rule for the write. The update is accepted only if the row still carries the version observed by the client. A competing update advances that version, so a stale writer affects zero rows instead of overwriting newer state.

Software Engineering Databases