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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 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 ...
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 ...
Deadlock prevention techniques and algorithms Name Coffman conditions Description Banker's algorithm: Mutual exclusion: The Banker's algorithm is a resource allocation and deadlock avoidance algorithm developed by Edsger Dijkstra. Preventing recursive locks: Mutual exclusion: This prevents a single thread from entering the same lock more than once.
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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).
A hierarchy of resources may be defined, so that a number of levels of locking can be implemented. For instance, a hypothetical database might define a resource hierarchy as follows: Database; Table; Record; Field; A process can then acquire locks on the database as a whole, and then on particular parts of the database. A lock must be obtained ...
A precedence graph, also named conflict graph [1] and serializability graph, is used in the context of concurrency control in databases. [2] It is the directed graph representing precedence of transactions in the schedule, as reflected by precedence of conflicting operations in the transactions.