[hibernate-dev] PESSIMISTIC_FORCE_INCREMENT lock mode

[Arnold Gálovics]

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 at 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 at 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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>
>