It will be distributed in TheServerSide.com's new newsletter, which should
be emailed by the end of the week. If you want to get the article, just
signup as a member of TheServerSide.com.
Floyd
-----Original Message-----
From: A mailing list for Enterprise JavaBeans development
[mailto:[EMAIL PROTECTED]]On Behalf Of Danny Trieu
Sent: Wednesday, September 20, 2000 9:27 AM
To: [EMAIL PROTECTED]
Subject: Re: how about a definitive defintion of optimistic and
pessimisticconcurrency
May I know which which megazine this article will be posted?
Floyd Marinescu wrote:
> Hi everyone,
>
> I am preparing a short article on advanced entity bean topics and
I would
> like to confirm some confusing definitions with you.
>
> Pessimistic and Optimistic Concurrency
> Algorithms used by a database to handle concurrent access to data. With
> pessimistic concurrency, only one transaction can use a row in the db at a
> time (depending on isolation level). With optimistic, there is no locking
> going on, but transactional collisions/diamonds are detected and
appropriate
> transactions are rolled bac.
>
> One entity bean per PK in memory vs. multiple
> This is simply a design decision used by application servers on how to
> handle entity beans. App. servers like weblogic have only one entity bean
> per PK in memory, thus all access to the entity bean is serialized. Other
> app. servers allow multiple instances per pk to be in memory, and rely on
> the database to do isolation control.
>
> 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?
>
> thanks everyone,
>
> Floyd
>
> ---------------------------------
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