What are the benefits and drawbacks of using optimistic concurrency control with ORM?

1 Database transactions

A database transaction is a unit of work that consists of one or more operations on the database, such as inserting, updating, deleting, or querying data. A transaction should follow the ACID properties: atomicity, consistency, isolation, and durability. Atomicity means that either all the operations in a transaction are executed or none of them are. Consistency means that the database remains in a valid state after each transaction. Isolation means that each transaction is executed as if it were the only one running on the database. Durability means that the effects of a transaction are permanent and cannot be lost due to system failures.

2 Concurrency control

Concurrency control is the process of managing multiple transactions that access the same data at the same time. Concurrency control ensures that the transactions do not interfere with each other and maintain the consistency and integrity of the database. However, concurrency control can also introduce some problems, such as deadlocks, conflicts, and performance issues. Deadlocks occur when two or more transactions are waiting for each other to release a resource they need. Conflicts occur when two or more transactions try to modify the same data and cause inconsistency or data loss. Performance issues occur when concurrency control mechanisms cause too much overhead or delay in the execution of transactions.

3 ORM and concurrency control

ORM frameworks usually provide some built-in features or options for handling concurrency control. For example, some ORM frameworks support different transaction isolation levels, such as read committed, repeatable read, or serializable, that determine how much data visibility and consistency a transaction has. Some ORM frameworks also support different locking mechanisms, such as pessimistic locking or optimistic locking, that determine how a transaction prevents or resolves conflicts with other transactions.

4 Optimistic locking

Optimistic locking is a concurrency control strategy that assumes that conflicts are rare and allows transactions to proceed without acquiring locks on the data they access or modify. Instead, optimistic locking relies on a versioning mechanism that tracks the changes made by each transaction and detects any conflicts at the end of the transaction. If a conflict is detected, the transaction is aborted and rolled back, and the application can retry or handle the error.

6 Drawbacks of optimistic locking with ORM

One of the main drawbacks of using optimistic locking with ORM is that it can increase the complexity and error handling of the application. Optimistic locking requires the application to implement a versioning mechanism, such as adding a timestamp or a version number column to the database tables, and to check for conflicts at the end of each transaction. Optimistic locking also requires the application to handle the possibility of transaction failures and rollbacks, and to decide how to retry or recover from them. Optimistic locking can also lead to data loss or inconsistency, if the conflicts are not detected or resolved properly.