PRAM consistency
Encyclopedia
PRAM consistency also known as FIFO
consistency
, or Processor
consistency
.
All processes
see memory
writes from one process in the order they were issued from the process.
Writes from different processes may be seen in a different order on different processes. Only the write order needs to be consistent, thus the name pipelined.
PRAM consistency is easy to implement. In effect it says that there are no guarantees about the order in which different processes see writes, except that two or more writes from a single source must arrive in order, as though they were in a pipeline.
P1:W(x)1
P2: R(x)1W(x)2
P3: R(x)1R(x)2
P4: R(x)2R(x)1
Time ---->
Fig: A valid sequence of events for PRAM consistency.
The above sequence is not valid for Causal consistency
because W(x)1 and W(x)2 are causal, so different processes must read it in the same sequence.
FIFO
FIFO is an acronym for First In, First Out, an abstraction related to ways of organizing and manipulation of data relative to time and prioritization...
consistency
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...
, or Processor
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
consistency
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...
.
All processes
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
see memory
Computer storage
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
writes from one process in the order they were issued from the process.
Writes from different processes may be seen in a different order on different processes. Only the write order needs to be consistent, thus the name pipelined.
PRAM consistency is easy to implement. In effect it says that there are no guarantees about the order in which different processes see writes, except that two or more writes from a single source must arrive in order, as though they were in a pipeline.
P1:W(x)1
P2: R(x)1W(x)2
P3: R(x)1R(x)2
P4: R(x)2R(x)1
Time ---->
Fig: A valid sequence of events for PRAM consistency.
The above sequence is not valid for Causal consistency
Causal consistency
Causal consistency is one of the consistency models used in the domain of the concurrent programming ....
because W(x)1 and W(x)2 are causal, so different processes must read it in the same sequence.