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Also known as: OCC
A concurrency method that assumes few conflicts, allowing transactions to proceed and validating for conflicts at commit time.
DESCRIPTION
Optimistic Concurrency Control avoids locks during transaction execution, improving throughput in low-contention environments. Transactions proceed and validate read-write sets at commit, aborting on conflicts. Typical implementations use version numbers or timestamps to detect write skew. OCC suits distributed systems and user-driven workloads where contention is rare. It contrasts with pessimistic locking, which prevents conflicts by acquiring locks up front.
ALTERNATIVE DEFINITIONS
Wikipedia
Optimistic concurrency control (OCC), sometimes called optimistic locking, is a concurrency control method applied to transactional systems.
Introduces the method and alternate term optimistic locking.
Microsoft Learn
Optimistic concurrency allows multiple processes to make changes to data and detects conflicts when an update is attempted.
Focuses on detection via concurrency tokens in application frameworks.
RELATED TERMS
Multiversion Concurrency Control Two-Phase Locking Transaction Isolation Levels Conflict Detection Versioning Deadlock Compare-and-Swap Commit Validation
COMPETING TERMS
Pessimistic Concurrency Control
KNOWLEDGE AREAS
Data Storage & Operations Software Engineering Data Engineering Data Architecture
TARGET AUDIENCE
Software Developer Data Engineer Data Architect Cloud Architect Data Modeler
EXTERNAL SOURCES
- Wikipedia - Optimistic concurrency control
- Martin Fowler - Pattern: Optimistic Offline Lock
- Oracle - Oracle docs on concurrency approaches
- PostgreSQL - MVCC reference for comparison
TOP QUESTIONS
When should Optimistic Concurrency Control be used?
Use OCC when contention is low, such as user-driven updates or distributed services with sparse conflicts. It yields higher throughput by avoiding locks during execution.
Category: Requirements
How does Optimistic Concurrency Control detect conflicts?
It validates read and write sets at commit using timestamps or version numbers. If another transaction has modified data, the commit fails and the transaction retries.
Category: Concepts
What is the main difference between OCC and pessimistic locking?
OCC defers conflict handling to commit-time checks; pessimistic locking prevents conflicts up front by acquiring locks, potentially reducing concurrency.
Category: Comparison
What are common OCC pitfalls?
High contention can cause frequent retries and degraded performance. Poor validation logic risks undetected conflicts and lost updates.
Category: Mistakes
How is OCC implemented in practice?
Systems track version identifiers per record and compare on update. Frameworks like EF Core use concurrency tokens to detect conflicts automatically.
Category: HowTo
Why is OCC relevant in distributed systems?
It avoids distributed locks and can scale better when conflicts are infrequent, reducing coordination overhead.
Category: Relevancy
Does OCC eliminate deadlocks?
Yes, OCC avoids deadlocks because it doesn’t hold locks during execution. However, it may increase transaction retries under contention.
Category: Misunderstanding
What workloads are a poor fit for OCC?
High-contention transactional workloads, hot rows, and intensive concurrent updates often favor pessimistic locking or partitioning strategies.
Category: Risk
How do isolation levels interact with OCC?
OCC can complement higher isolation levels by validating conflicts at commit, but strong isolation may still require careful design to avoid anomalies.
Category: Opinion