Floyd Marinescu wrote:
> The confusing part here is why people on this list insist on calling
> Weblogic's one-entity-per-pk strategy "pessimistic concurrency", and other
> app. server's multiple-entity's-per-pk strategy "Optimistic Concurrency". I
> thought that the terminology pessimistic/optimistic apply only to database
> issues. How exactly can these terms be used when describing app. servers?
>
Concurrency control is used in any system that has to deal with possible conflicting
changes to the same data. Critical sections in a multi-threaded application are
usually protected by locks (semaphore or mutex). Concurrent C also uses database like
concepts for communication between parallel processes. It may be confusing to use the
same terms in a new way, but we are dealing with concurrent changes to persistent
data. So database terms seem appropriate.
IMO, pessimistic concurrency refers to the situation where requests for a resource
are blocked if the resource is currently in use. Optimistic concurrency refers to the
situation where concurrent access to a resource is allowed, but conflicts are
detected at a later synchronization point (transaction commit).
>
> thanks everyone,
>
> Floyd
>
--Victor
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