Immediate consistency
Encyclopedia
Immediate consistency is one of the consistency model
s used in the domain of parallel programming, in contrast to eventual consistency
. The term "immediate" refers not to updates not taking any time to perform, but simply to the fact that when an update operation returns to the user with a successful result, the result of that update is immediately visible to all observers. Non-replicated distributed data storage systems, or non-distributed data storage systems such as traditional centralized databases, tend to provide immediate consistency, as there is only one location at which to update the data, rather than multiple copies; also, distributed replicated systems using synchronous replication offer immediate consistency by forcing the user to wait until confirmation of the update has been received (or inferred) from every replica of the data.
Immediate consistency defines only the state of the system with regard to a single update, after the update has been reported to the user as completed; it does not define the state of the system that might be observed while an update is in progress (e.g., to other users of the system). Therefore, it does not imply sequential consistency
or strict consistency, but is not incompatible with them.
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 parallel programming, in contrast to eventual consistency
Eventual consistency
Eventual consistency is one of the consistency models used in the domain of parallel programming, for example in distributed shared memory, distributed transactions, and optimistic replication, it means that given a sufficiently long period of time over which no changes are sent, all updates can be...
. The term "immediate" refers not to updates not taking any time to perform, but simply to the fact that when an update operation returns to the user with a successful result, the result of that update is immediately visible to all observers. Non-replicated distributed data storage systems, or non-distributed data storage systems such as traditional centralized databases, tend to provide immediate consistency, as there is only one location at which to update the data, rather than multiple copies; also, distributed replicated systems using synchronous replication offer immediate consistency by forcing the user to wait until confirmation of the update has been received (or inferred) from every replica of the data.
Immediate consistency defines only the state of the system with regard to a single update, after the update has been reported to the user as completed; it does not define the state of the system that might be observed while an update is in progress (e.g., to other users of the system). Therefore, it does not imply sequential consistency
Sequential consistency
Sequential consistency is one of the consistency models used in the domain of concurrent programming . It was first defined as the property that requires that ".....
or strict consistency, but is not incompatible with them.