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In a SQL database, a record is typically called a "row". The introduction of granular (subset) locks creates the possibility for a situation called deadlock. Deadlock is possible when incremental locking (locking one entity, then locking one or more additional entities) is used. To illustrate, if two bank customers asked two clerks to obtain ...
A wait-for graph in computer science is a directed graph used for deadlock detection in operating systems and relational database systems.. In computer science, a system that allows concurrent operation of multiple processes and locking of resources and which does not provide mechanisms to avoid or prevent deadlock must support a mechanism to detect deadlocks and an algorithm for recovering ...
In databases and transaction processing, two-phase locking (2PL) is a pessimistic concurrency control method that guarantees conflict-serializability. [1] [2] It is also the name of the resulting set of database transaction schedules (histories).
This subtlety can increase the chance that a programmer will unknowingly introduce a deadlock. [citation needed] In a database management system, for example, a lock could protect, in order of decreasing granularity, part of a field, a field, a record, a data page, or an entire table. Coarse granularity, such as using table locks, tends to give ...
For example, transaction A may access portion X of the database, and transaction B may access portion Y of the database. If at that point, transaction A then tries to access portion Y of the database while transaction B tries to access portion X, a deadlock occurs, and neither transaction can move forward. Transaction-processing systems are ...
Phantom deadlocks are deadlocks that are falsely detected in a distributed system due to system internal delays but do not actually exist. For example, if a process releases a resource R1 and issues a request for R2 , and the first message is lost or delayed, a coordinator (detector of deadlocks) could falsely conclude a deadlock (if the ...
occurrence of deadlock in distributed system. P 1 initiates deadlock detection. C 1 sends the probe saying P 2 depends on P 3. Once the message is received by C 2, it checks whether P 3 is idle. P 3 is idle because it is locally dependent on P 4 and updates dependent 3 (2) to True. As above, C 2 sends probe to C 3 and C 3 sends probe to C 1.
Banker's algorithm is a resource allocation and deadlock avoidance algorithm developed by Edsger Dijkstra that tests for safety by simulating the allocation of predetermined maximum possible amounts of all resources, and then makes an "s-state" check to test for possible deadlock conditions for all other pending activities, before deciding whether allocation should be allowed to continue.