Re: Selective commit

From: Andrus Adamchik (andru..bjectstyle.org)
Date: Mon Jan 07 2008 - 10:41:03 EST

  • Next message: hmai..otmail.ru: "Several questions about Cayenne"

    It's not that expensive (each context attaches to a shared stack) and
    looks like the best strategy in your case.

    One possible optimization is to use a single shared DataContext for
    read-only operations, and create a new DataContext for each operation
    that is expected to modify and commit the objects. It is only possible
    of course if you have any "read-only" operations at all.

    Andrus

    On Jan 7, 2008, at 5:30 PM, Álvaro Martínez wrote:

    >
    > Thanks, Andrus and Philip
    >
    > The threads I'm talking about are created from many sources and for
    > different reasons. Not of all them are triggered in response to
    > "something". There are also watchers, periodic tasks... So I can't
    > map data contexts to some particular condition.
    >
    > So then I have to create one data context per operation (that means
    > a set of actions). Is this expensive? We are developing a heavy
    > loaded cluster of servers, so it's important.
    >
    > Thanks again!
    >
    >
    > Andrus Adamchik escribió:
    >> Hi Álvaro,
    >>
    >> It is hard to give a precise advice on multithreading without
    >> knowing the nature of your application. So here is a few general
    >> notes:
    >>
    >> * DataContext instance is your isolated area for making in-memory
    >> changes to objects that will all be committed at once. So consider
    >> using multiple contexts as appropriate. Cayenne docs recommend
    >> various common patterns, such as DataContext per session (i.e. each
    >> user has a dedicated context), DataContext per request, or
    >> DataContext per application (in a read-only app). You can also
    >> devise your own approach, if none of the above fit your needs. All
    >> you need to know here is that multiple threads *reading* from a
    >> shared DataContext is ok, but multiple threads *writing* to a
    >> shared DataContext is not ok.
    >>
    >> * In a rare case if you really need multiple threads to work off of
    >> the same context, consider using a dedicated nested DataContext for
    >> each atomic object modifications.
    >>
    >> Andrus
    >>
    >>
    >> On Jan 7, 2008, at 2:44 PM, Álvaro Martínez wrote:
    >>>
    >>> Hi, I've been working for a while with Cayenne but never realized
    >>> I had a problem... until I got a weird exception.
    >>>
    >>> The fact is that I had been using context.newObject() and
    >>> context.commitChanges() to create new rows in the database. But my
    >>> application works with many threads, so global commits can (and in
    >>> fact do) interrupt normal creation of objects. Thread A and Thread
    >>> B are creating objects and filling their fields, but then B
    >>> commits all and A throws a validation exception because mandatory
    >>> fields are missing.
    >>>
    >>> How could I commit only one object?
    >>>
    >>> Thanks,
    >>>
    >>> Álvaro from Spain (Push the button Inc.)
    >>>
    >>>
    >>>
    >>
    >>
    >>
    >
    >



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