AW: Optimistic locking

From: Peter Schröder (Peter.Schroede..reenet-ag.de)
Date: Wed Apr 11 2007 - 03:45:06 EDT

  • Next message: Marc Gabriel-Willem: "RE: Optimistic locking"

    hi marc,

    if both threads are notified of the update, there should be no need of the optimistic locking. you may use javas synchronization instead.
    but i am somewhat surprised that two different data-contexts are notified of a change of one object.

    kind regards,
    peter

    -----Ursprüngliche Nachricht-----
    Von: Marc Gabriel-Willem [mailto:marc.gabriel-wille..ide-international.com]
    Gesendet: Mittwoch, 11. April 2007 09:34
    An: use..ayenne.apache.org
    Betreff: RE: Optimistic locking

    Thank you for your reply.

    For information, I'm working on a JSF web application.
    I was doing test using two different browsers (Firefox + IE) in order to
    avoid session management problem.

    Your document describes the optimistic locking as a mechanism that
    detects update done using an external application (SQL+, etc). For that
    situation, regarding the Cayenne log file, I can tell you it is ok, it
    works.

    My concern was the concurrency management in the same Cayenne
    application (for example, 2 users using the same application and
    modifying the same DataObject !).

    In that situation, Cayenne does not raise error... Is it normal ?
    Should I use the "snapshot version" data to check if something has
    changed since the beginning of the user modification ?

    Thank you
    Marc

    -----Original Message-----
    From: Michael Gentry [mailto:blacknex..mail.com]
    Sent: Tuesday, April 10, 2007 5:37 PM
    To: use..ayenne.apache.org
    Subject: Re: Optimistic locking

    In a lot of web applications (JSP, Struts, Tapestry, ...) the session is
    usually stored as a cookie in the browser, so opening a new browser
    window
    and re-connecting to the application won't give you a new session and
    therefore you'd be connected to the original session (and DataContext --
    I'm
    assuming you are storing the DC in the session) with the updated values.
    Try your test using different concurrent browsers, such as Firefox and
    IE/Safari (for example) and see if you get the same results. I use
    optimistic locking on pretty much everything and haven't noticed a
    problem.
    I wrote this a long time ago, too, which may or may not help:

    http://cwiki.apache.org/CAY/optimistic-locking-explained.html

    I'll be out-of-touch for most of the rest of the day, but if you still
    have
    problems, perhaps someone else on the list can help.

    Thanks,

    /dev/mrg

    On 4/10/07, Marc Gabriel-Willem
    <marc.gabriel-wille..ide-international.com>
    wrote:
    >
    > Hi,
    >
    >
    >
    > I have some trouble with the optimistic locking function.
    >
    > I set the 'optimistic locking' option to an ObjEntity and moreover I
    set
    > an attribute as "used for locking".
    >
    >
    >
    > I'm in a web environment.
    >
    >
    >
    > When I do some modification in a DataObject, the 'log' displayed by
    > Cayenne displays properly the query using the attribute for locking
    > check.
    >
    > But, when a concurrent client modifies the 'same' DataObject, no error
    > is detected ... because the new value for the optimistic check is
    used.
    >
    >
    >
    > It is important to note that the DataObject is modified by different
    > browser (so different session data context) and by different child
    data
    > context !
    >
    >
    >
    > Scenario:
    >
    >
    >
    > My original record > attr1=MyAttr1, attr2=10:15:10
    >
    > My record modified by client #1> attr1=MyAttr2,
    > attr2(UseForLock)=10:18:15 [ attrSpecifiedInWhereClause: 10:15:10 ]
    >
    > My record modified by client #2> attr1=MyAttr3,
    > attr2(UseForLock)=10:19:40 [ attrSpecifiedInWhereClause: 10:18:15 ]
    >
    >
    >
    > The value of the attribute used for optimistic locking seems to be
    > refreshed...
    >
    >
    >
    > Thank you,
    >
    > Marc
    >
    >



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