Editing Consistency model (section)

=== Strict consistency ===

Strict consistency is the strongest consistency model. Under this model, a write to a variable by any processor needs to be seen instantaneously by all processors.

The strict model diagram and non-strict model diagrams describe the time constraint – instantaneous. It can be better understood as though a global clock is present in which every write should be reflected in all processor caches by the end of that clock period. The next operation must happen only in the next clock period.  

In the following diagram, P means "process" and the global clock's value is represented in the Sequence column.  
{| class="wikitable"
|-
! rowspan=2 | Sequence
! colspan=2 | Strict model
! colspan=2 | Non-strict model
|-
! {{abbr|P|Processor}}1
! {{abbr|P|Processor}}2
! {{abbr|P|Processor}}1
! {{abbr|P|Processor}}2
|-
! 1
| ''W''(''x'')1
|
| ''W''(''x'')1
|
|-
! 2
|           
| ''R''(''x'')1

|
| ''R''(''x'')0
|-
! 3
|
|           
|     
| ''R''(''x'')1
|}

This is the most rigid model. In this model, the programmer's expected result will be received every time. It is deterministic. Its practical relevance is restricted to a thought experiment and formalism, because instantaneous message exchange is impossible. It doesn't help in answering the question of conflict resolution in concurrent writes to the same data item, because it assumes concurrent writes to be impossible.