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From Jean-Louis Monteiro <jlmonte...@tomitribe.com>
Subject Re: question around entityManager.flush
Date Wed, 21 May 2014 15:11:16 GMT
I don't see why, except if you are explicitly checking for database
constraints in your code.
Because, the default JDBC connection isolation level is READ COMMITTED
AFAIR or REPEATABLE_READ for MySQL.

Anyway, that means that you can never read uncommitted data.

JLouis

--
Jean-Louis Monteiro
http://twitter.com/jlouismonteiro
http://www.tomitribe.com


On Wed, May 21, 2014 at 7:58 AM, Howard W. Smith, Jr. <
smithh032772@gmail.com> wrote:

> removing the manual/forced entityManager.flush() broke my app in a few
> places. reverting to previous version and I may try to revisit this later.
> :)
>
>
>
> On Wed, May 21, 2014 at 10:00 AM, Howard W. Smith, Jr. <
> smithh032772@gmail.com> wrote:
>
> > Thanks Jean-Louis. Based on your response, i just commented out
> > entityManager.flush() in my AbstractFacade.java for create, edit, and
> > remove methods.
> >
> > i did some testing in my app, and seems to work well. will see how my app
> > performs under load and when users are logged in and working,
> concurrently.
> >
> > thanks again.
> >
> >
> >
> > On Wed, May 21, 2014 at 5:21 AM, Jean-Louis Monteiro <
> > jlmonteiro@tomitribe.com> wrote:
> >
> >> As a general rule, I would recommend to never call flush(). The JPA
> >> provider optimizing the flushing to avoid connections between the
> >> Persistence Context and the rdbms.
> >>
> >> Of course at least at the end of the transaction (commit) the JPA
> provider
> >> flushes.
> >> But for example, when you have a loop with search, read, update .... the
> >> JPA provider is able to detect that there is a risk of dealing with
> stale
> >> object and will therefor flush as well.
> >>
> >> The only case I call flush is basically when as mentioned already, I
> need
> >> to check database constraints (Unique, etc).
> >> The only reason is that I want to explicitly catch the exception either
> to
> >> ignore, retry, or rethrow using a business exception.
> >>
> >> Sometimes, I also use an ejb with a REQUIRES_NEW, so that the current
> >> transaction is suspended and a new one is created. Then, if an exception
> >> occurs at commit time, I can catch in the current bean without changing
> >> the
> >> status of the current transaction.
> >>
> >> JLouis
> >>
> >>
> >>
> >> --
> >> Jean-Louis Monteiro
> >> http://twitter.com/jlouismonteiro
> >> http://www.tomitribe.com
> >>
> >>
> >> On Mon, May 19, 2014 at 8:47 AM, Howard W. Smith, Jr. <
> >> smithh032772@gmail.com> wrote:
> >>
> >> > Interesting question and answer.
> >> >
> >> > Per my 2+ year experience with Java EE 6, in my app, i used NetBeans
> to
> >> > develop my JPA session facade (@EJB JPA DAO) classes, including
> abstract
> >> > class. In the abstract class, in the create and edit methods, I did
> add
> >> > flush(), so after every create and edit JPA request, data is written
> >> > immediately.
> >> >
> >> > Honestly, I don't have any need to use @Scheduler or timer methods to
> >> > ensure data is saved....successfully.
> >> >
> >> > In fact, I can maybe even remove flush(), but I have not done that
> >> (yet).
> >> > If I did remove flush() in my abstract class, then I would need to
> test
> >> the
> >> > app, accordingly, to see the impact.
> >> >
> >> > I really don't see any performance issues with my
> >> approach/implementation,
> >> > but the app does not have many concurrent
> >> > users/database-update-requests/etc.
> >> >
> >> >
> >> >
> >> > On Mon, May 19, 2014 at 4:02 AM, Andy Gumbrecht <
> >> agumbrecht@tomitribe.com
> >> > >wrote:
> >> >
> >> > > Hi there Radhakrishna,
> >> > >
> >> > >
> >> > > On 19/05/2014 08:15, Radhakrishna Kalyan wrote:
> >> > >
> >> > >> Hi,
> >> > >>
> >> > >> I have question around entityManager.flush().
> >> > >> Is it ok to call multiple times? Or will there be any performance
> >> issue.
> >> > >>
> >> > > Every time you hit the the database you will take a performance hit
> >> back
> >> > -
> >> > > How much is impossible to say and is very dependant on what your app
> >> is
> >> > > doing. Just always think along the lines of 'how can I do this with
> >> less'
> >> > > and you'll be fine.
> >> > >
> >> > >
> >> > >> My case is, I have a timer service which executes periodically
> where
> >> I
> >> > >> create a database entity using a dao object using
> >> > entityManager.persist(),
> >> > >> after that I also  call entityManager.flush().
> >> > >>
> >> > >> The reason to do so is, if database commit fails due to certain
> >> reason
> >> > >> like
> >> > >> unique constrain exception then I want the timer service to send
a
> >> JMS
> >> > >> message.
> >> > >>
> >> > > What you are doing is not necessarily wrong, but why not just let
> the
> >> > > container do the work for you. The container managed transactions
> are
> >> > your
> >> > > friend.
> >> > >
> >> > >
> >> > >> If I don't call entityManager.flush() then I am not able to catch
> any
> >> > >> exception in my timer service thus fails to send any JMS message.
> >> > >>
> >> > > In your service look up another local bean that handles the
> >> persistence
> >> > >  and if required sends a message on success, this will all run in
a
> >> > > transacted context - The success message will only be sent if the
> bean
> >> > > method actually completes.
> >> > > If the bean method call fails then you can catch the error and do
> the
> >> > > extra leg work to send the 'fail' message.
> >> > >
> >> > >
> >> > >> However at the end the database entity is never created which
is
> >> > correct.
> >> > >> But if I can't able to send the JMS message upon exception then
I
> >> does
> >> > not
> >> > >> meet the requirement.
> >> > >>
> >> > >> Any ideas or recommendations to do it in a better way
> >> > >>
> >> > >>
> >> > >>  So I guess my suggestion is to not try and do all the work in
the
> >> timer
> >> > > service method, rather call another bean method do do the work.
> >> > >
> >> > > Andy.
> >> > >
> >> > > --
> >> > >   Andy Gumbrecht
> >> > >
> >> > >   http://www.tomitribe.com
> >> > >   agumbrecht@tomitribe.com
> >> > >   https://twitter.com/AndyGeeDe
> >> > >
> >> > >   TomEE treibt Tomitribe! | http://tomee.apache.org
> >> > >
> >> > >
> >> >
> >>
> >
> >
>

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