Re: [hibernate-dev] PESSIMISTIC_FORCE_INCREMENT lock mode
Hey,
I'm still a bit uncertain about this, as I only tested this lock mode with
H2 which as far as I know is not supporting shared locks, so it will
automatically acquire an exclusive lock. That is a possibility why I've
seen the FOR UPDATE clause at the end of the SELECT statement.
*My question rather is:* what's the intended behavior of this lock mode?
Okay, it's a pessimistic lock with incrementing the version number
automatically at locking time. What type of lock will it acquire? Shared or
exclusive?
I think this is important and it should be really mentioned in the
Hibernate docs as now it's a bit confusing. The JPA spec is also unclear
for me about this lock mode.
Thank you guys for helping me out!
Best Regards,
Arnold
On Fri, Jul 28, 2017 at 7:40 AM, Vlad Mihalcea <mihalcea.vlad(a)gmail.com>
wrote:
That's how Hibernate was executing the statements when I wrote
the article.
I spotted the difference when writing the book, but didn't have time to
update the article.
I changed the SQL output to reflect the current behavior which adds a FOR
UPDATE clause when fetching the entity.
I also rephrased that sentence since it's no longer relevant to the
current behavior.
Vlad
On Thu, Jul 27, 2017 at 4:46 PM, Arnold Gálovics <galovicsarnold(a)gmail.com
> wrote:
> Hi all,
>
> I'm a bit confused with the mentioned lock mode.
>
> *The doc says the following:*
> *"The entity is locked pessimistically and its version is incremented
> automatically even if the entity has not changed."*
>
> I'm checking this with an H2 DB and the current behavior is the following:
> - the version attribute is incremented in advance, right after fetching
> (I'm using EntityManager#find here, but with lock, it should be the same)
> - the original fetching query contains the SELECT ... FOR UPDATE clause
>
> Knowing this, it seems for me that this lock mode involves a DB lock,
> however the doc doesn't say anything about this, especially whether it's a
> shared or exclusive lock.
>
> I've checked Vlad's article about this.
> https://vladmihalcea.com/2015/02/16/hibernate-locking-patter
> ns-how-does-pessimistic_force_increment-lock-mode-work/
>
> It says the following: "*The PESSIMISTIC_FORCE_INCREMENT naming might lead
> you into thinking that you are using a pessimistic locking strategy, while
> in reality this Lock Mode is just an optimistic locking variation."*
>
> So now I'm unsure what this really is.
>
> Could you please briefly describe it to me if I missed something?
>
> Thanks in advance!
>
> Best Regards,
> Arnold
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