What is lock based concurrency?
It is a mechanism in which a transaction cannot read or write data unless the appropriate lock is acquired. This helps in eliminating the concurrency problem by locking a particular transaction to a particular user.
How concurrency is controlled using lock based protocols?
Lock-based protocols manage the order between the conflicting pairs among transactions at the time of execution, whereas timestamp-based protocols start working as soon as a transaction is created. Every transaction has a timestamp associated with it, and the ordering is determined by the age of the transaction.
What is a locking protocol?
Locking protocols are used in database management systems as a means of concurrency control. Multiple transactions may request a lock on a data item simultaneously. Hence, we require a mechanism to manage the locking requests made by transactions. Such a mechanism is called as Lock Manager.
How concurrency control is done in distributed system?
Concurrency control is the activity of co- ordinating concurrent accesses to a data- base in a multiuser database management system (DBMS). Concurrency control per- mits users to access a database in a multi- programmed fashion while preserving the illusion that each user is executing alone on a dedicated system.
What is 2 phase locking protocol?
A transaction is said to follow the Two-Phase Locking protocol if Locking and Unlocking can be done in two phases. Growing Phase: New locks on data items may be acquired but none can be released. Shrinking Phase: Existing locks may be released but no new locks can be acquired.
What are two problems of lock based protocols?
Problems associated with Simple locking: Data inconsistency between multiple transactions. Deadlock, a situation where the transactions try to access lock on already locked data items. No guarantee of serializability (i.e. execution of a concurrent transaction equivalent to that of a transaction executed serially)
What are the deadlock prevention protocols?
Deadlock can be prevented by eliminating any of the four necessary conditions, which are mutual exclusion, hold and wait, no preemption, and circular wait. Mutual exclusion, hold and wait and no preemption cannot be violated practically.
What are locks in distributed system?
A lock is a variable associated with a data item that determines whether read/write operations can be performed on that data item. Generally, a lock compatibility matrix is used which states whether a data item can be locked by two transactions at the same time.
What are concurrency control protocols?
The concurrency control protocols ensure the atomicity, consistency, isolation, durability and serializability of the concurrent execution of the database transactions. Therefore, these protocols are categorized as: Lock Based Concurrency Control Protocol.
What is shared and exclusive locks?
An exclusive or write lock gives a process exclusive access for writing to the specified part of the file. While a write lock is in place, no other process can lock that part of the file. A shared or read lock prohibits any other process from requesting a write lock on the specified part of the file.
Why do we use lock based protocol?
It is the simplest way of locking the data while transaction. Simplistic lock-based protocols allow all the transactions to get the lock on the data before insert or delete or update on it. It will unlock the data item after completing the transaction.
How can we prevent deadlock in distributed system?
There are 2 ways to prevent deadlock in a distributed system….Deadlock Prevention Policies in Distributed System
- Mutual Exclusion: There is at least one resource that is non-sharable and can be used by only one Process at a time.
- Hold and Wait: A process is holding at least one Resource and waiting for another.