What are pessimistic and optimistic locking?
There are two models for locking data in a database: Optimistic locking , where a record is locked only when changes are committed to the database. Pessimistic locking , where a record is locked while it is edited.
How do you do optimistic locking?
In order to use optimistic locking, we need to have an entity including a property with @Version annotation. While using it, each transaction that reads data holds the value of the version property. Before the transaction wants to make an update, it checks the version property again.
What is the use of optimistic locking?
Optimistic locking is a technique for SQL database applications that does not hold row locks between selecting and updating or deleting a row. The application is written to optimistically assume that unlocked rows are unlikely to change before the update or delete operation.
What’s pessimistic locking?
Pessimistic concurrency control (or pessimistic locking) is called “pessimistic” because the system assumes the worst — it assumes that two or more users will want to update the same record at the same time, and then prevents that possibility by locking the record, no matter how unlikely conflicts actually are.
What is the difference between pessimistic and optimistic updates?
Optimistic locking is when you check if the record was updated by someone else before you commit the transaction. Pessimistic locking is when you take an exclusive lock so that no one else can start modifying the record.
How do you handle optimistic concurrency?
The general approach to handle a concurrency conflicts is:
- Catch DbUpdateConcurrencyException during SaveChanges .
- Use DbUpdateConcurrencyException.
- Refresh the original values of the concurrency token to reflect the current values in the database.
- Retry the process until no conflicts occur.
Could you explain the difference between optimistic vs pessimistic locking?
What is optimistic and pessimistic locking in mysql?
Optimistic concurrency control (OCC) allows multiple transactions to modify data without interfering with each other. Pessimistic concurrency control: when a transaction is modifying data, pessimistic locking applies a lock to the data so other transactions can’t access the same data.
What is optimistic lock exception?
If you get an optimistic locking exception, it means that some other transaction has committed changes to entities you were trying to update/delete. Since the other transaction has committed, retrying immediately might have a good chance to succeed.
How can we do pessimistic locking in Entity Framework?
entity framework 6 and pessimistic concurrency
- Creation a transactionScope around my DbContext with serialised isolation level.
- Create a DbContext.
- Do some reads.
- Do some changes to objects.
- Call SaveChanges on the DbContext.
- Commit the transaction scope (thus saving the changes)
What is IsConcurrencyToken?
The IsConcurrencyToken method is used to specify that a property should be included in a WHERE clause in an UPDATE or DELETE statement as part of concurrency management.
What’s the difference between optimistic and pessimistic locking?
Pessimistic Locking: It assumes the worst. It thinks conflicts are very likely to happen. So it locks as early as it can. Optimistic Locking: It assumes conflicts are unlikely to happen, though it might happen. So it locks as late as it can. Pessimistic locking provides better integer with the cost of performance.
How is pessimistic locking used in SQL Server?
This is a standard locking like an Exclusive lock or Shared lock. The reader is blocked by writer and writer is blocked by the reader. SQL Server Isolation levels like Read Committed, Repeatable Read, Serializable are mostly doing Pessimistic Locking.
Why is the lost update anomaly generated in pessimistic locking?
The reads and the writes are interleaves, and that’s why the Lost Update anomaly is generated. Pessimistic locking aims to avoid conflicts by using locking. In the diagram above, both Alice and Bob will acquire a read (shared) lock on the account table row upon reading it.
Why do we use pessimistic locking in OLTP?
The big OLTP system like banking system or finance system are always preferred to use Pessimistic Locking because data accuracy is required for both reader and writer. Yes, locking is an extra overhead in a big system, but a few types of the application required for accuracy.
