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From "Daryl Stultz" <da...@6degrees.com>
Subject Re: EntityManager handling
Date Mon, 22 Dec 2008 20:06:41 GMT
>
> True. But closing EntityManager essentially will clear up its cache. For a
> higher performance, consider *not* closing EntityManager and pooling them,
> provided your application semantics allows for reuse of cached persistence
> instances from a different transaction.


Yikes! This is getting more complicated than I am prepared for. Where can I
find information on the best way to manage/pool EMs?

>
>
> > It seems the EM can detect when 2 objects representing the same row in
> the
>
> Not exactly. Let us say database has a row in PERSON table with primary key
> 'X'.
>
> Effectively, JVM now has two separate Java instances p1 and p2 in two
> separate caches of em1 and em2.


Yes I get how 2 instances of the same row can be had, but...

>
> If both em1 and em2 modify p1 and p2 respectively and attempts commit, then
> the later commit will fail.


...it's obviously not the EM instance that detects the concurrent mod, since
the 2 instances are in different EMs. What is the mechanism that does the
detection?

Thanks for your help.

-- 
Daryl Stultz
_____________________________________
6 Degrees Software and Consulting, Inc.
http://www.6degrees.com
mailto:daryl@6degrees.com

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