Sequential consistency
Encyclopedia
Sequential consistency is one of the consistency model
s used in the domain of concurrent programming (e.g. in distributed shared memory
, distributed transactions, etc.). It was first defined as the property that requires that "... the result of any execution is the same as if the operations of all the processors were executed in some sequential order, and the operations of each individual processor appear in this sequence in the order specified by its program."
The system provides sequential consistency if every node of the system sees the (write) operations on the same memory part (page, virtual object, cell, etc.) in the same order, although the order may be different from the order as defined by real time (as observed by hypothetical external observator or global clock) of issuing the operations.
The sequential consistency is weaker than strict consistency (which would demand that operations are seen in order in which they were actually issued, which is essentially impossible to secure in distributed system as deciding global time is impossible) and is the easiest consistency model to understand, since a system preserving that model is behaving in a way expected by an instantaneous system.
Consistency model
In computer science, consistency models are used in distributed systems like distributed shared memory systems or distributed data stores . The system supports a given model, if operations on memory follow specific rules...
s used in the domain of concurrent programming (e.g. in distributed shared memory
Distributed shared memory
Distributed Shared Memory , in Computer Architecture is a form of memory architecture where the memories can be addressed as one address space...
, distributed transactions, etc.). It was first defined as the property that requires that "... the result of any execution is the same as if the operations of all the processors were executed in some sequential order, and the operations of each individual processor appear in this sequence in the order specified by its program."
The system provides sequential consistency if every node of the system sees the (write) operations on the same memory part (page, virtual object, cell, etc.) in the same order, although the order may be different from the order as defined by real time (as observed by hypothetical external observator or global clock) of issuing the operations.
The sequential consistency is weaker than strict consistency (which would demand that operations are seen in order in which they were actually issued, which is essentially impossible to secure in distributed system as deciding global time is impossible) and is the easiest consistency model to understand, since a system preserving that model is behaving in a way expected by an instantaneous system.