External ID Upsert as a Race Condition Defense Strategy
How Database.upsert() with external ID fields prevents duplicate record creation in concurrent integration scenarios, and when additional concurrency controls are needed.
2 docs tagged with "concurrency"
View all tagsPreventing Duplicate Records with FOR UPDATE Locking in Concurrent Queueables
How concurrent Queueable jobs create race conditions that lead to duplicate records, and how FOR UPDATE locking, External ID Upsert, and dedup queries provide defense-in-depth.