Concurrency Control In Database Systems
Concurrency Control in Database Systems
Key Points
The purpose of concurrency control is to ensure that one user’s work does not inappropriately influence another user’s work. In some cases, these measures ensure that a user gets the same result when processing with other users as that person would have received if processing alone. In other cases, it means that the user’s work is influenced by other users but in an anticipated way.
When many transactions take place at the same time, they are called concurrent transactions. Managing the execution of such transactions is called concurrency control. As you can imagine, concurrency control is especially important in a multiuser database environment.
Deadlock:
When dealing with locks two problems can arise, the first of which being deadlock. Deadlock refers to a particular situation where two or more processes are each waiting for another to release a resource, or more than two processes are waiting for resources in a circular chain. Deadlock is a common problem in multiprocessing where many processes share a specific type of mutually exclusive resource. Some computers, usually those intended for the time-sharing and/or real-time markets, are often equipped with a hardware lock, or hard lock, which guarantees exclusive access to processes, forcing serialization. Deadlocks are particularly disconcerting because there is no general solution to avoid them.
A fitting analogy of the deadlock problem could be a situation like when you go to unlock your car door and your passenger pulls the handle at the exact same time, leaving the door still locked. If you have ever been in a situation where the passenger is impatient and keeps trying to open the door, it can be very frustrating. Basically you can get stuck in an endless cycle, and since both actions cannot be satisfied, deadlock occurs.
Livelock:
Livelock is a special case of resource starvation. A livelock is similar to a deadlock, except that the states of the
Key Points
The purpose of concurrency control is to ensure that one user’s work does not inappropriately influence another user’s work. In some cases, these measures ensure that a user gets the same result when processing with other users as that person would have received if processing alone. In other cases, it means that the user’s work is influenced by other users but in an anticipated way.
When many transactions take place at the same time, they are called concurrent transactions. Managing the execution of such transactions is called concurrency control. As you can imagine, concurrency control is especially important in a multiuser database environment.
Deadlock:
When dealing with locks two problems can arise, the first of which being deadlock. Deadlock refers to a particular situation where two or more processes are each waiting for another to release a resource, or more than two processes are waiting for resources in a circular chain. Deadlock is a common problem in multiprocessing where many processes share a specific type of mutually exclusive resource. Some computers, usually those intended for the time-sharing and/or real-time markets, are often equipped with a hardware lock, or hard lock, which guarantees exclusive access to processes, forcing serialization. Deadlocks are particularly disconcerting because there is no general solution to avoid them.
A fitting analogy of the deadlock problem could be a situation like when you go to unlock your car door and your passenger pulls the handle at the exact same time, leaving the door still locked. If you have ever been in a situation where the passenger is impatient and keeps trying to open the door, it can be very frustrating. Basically you can get stuck in an endless cycle, and since both actions cannot be satisfied, deadlock occurs.
Livelock:
Livelock is a special case of resource starvation. A livelock is similar to a deadlock, except that the states of the