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Sequential consistency is a consistency model used in the domain of concurrent computing (e.g. in distributed shared memory, distributed transactions, etc.).. It is the property 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 ...
A concurrent system is one where a computation can advance without waiting for all other computations to complete. [1] Concurrent computing is a form of modular programming. In its paradigm an overall computation is factored into subcomputations that may be executed concurrently.
Concurrent writes may be seen in a different order on different machines. This model relaxes sequential consistency on concurrent writes by a processor and on writes that are not causally related. Two writes can become causally related if one write to a variable is dependent on a previous write to any variable if the processor doing the second ...
Because computations in a concurrent system can interact with each other while being executed, the number of possible execution paths in the system can be extremely large, and the resulting outcome can be indeterminate. Concurrent use of shared resources can be a source of indeterminacy leading to issues such as deadlocks, and resource ...
Concurrency control mechanisms firstly need to operate correctly, i.e., to maintain each transaction's integrity rules (as related to concurrency; application-specific integrity rule are out of the scope here) while transactions are running concurrently, and thus the integrity of the entire transactional system.
Concurrent data structures are significantly more difficult to design and to verify as being correct than their sequential counterparts. The primary source of this additional difficulty is concurrency, exacerbated by the fact that threads must be thought of as being completely asynchronous: they are subject to operating system preemption, page faults, interrupts, and so on.
The happened-before relation is formally defined as the least strict partial order on events such that: If events a {\displaystyle a\;} and b {\displaystyle b\;} occur on the same process, a → b {\displaystyle a\to b\;} if the occurrence of event a {\displaystyle a\;} preceded the occurrence of event b {\displaystyle b\;} .
Linearizability is important in these concurrent systems where objects may be accessed by multiple processes at the same time and a programmer needs to be able to reason about the expected results. An execution of a concurrent system results in a history, an ordered sequence of completed operations.