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From Joe Baldwin <jfbald...@earthlink.net>
Subject Re: Standalone app, Threads and Object contexts
Date Wed, 02 May 2012 14:34:37 GMT
Not sure if this helps, but I have used both the default (Cayenne) connection pool, and DBCP.

	http://commons.apache.org/dbcp/

Cayenne's implementation seems to be adequate, but if you determine that you are going to
need something a bit more sophisticated, then DBCP is very reliable IMHO.  I have been using
DBCP for over a year and have had no issues yet (however, I also upgraded from MySQL 5.0 because
of connection bugs reported in parts of that version branch).

Joe



On May 2, 2012, at 10:18 AM, John Huss wrote:

> The number of ObjectContexts (or DataContexts) has no relation to the
> number of database connections.  ObjectContexts are cheap to create and
> use, so go wild.  Cayenne will do connection pooling out of the box by
> using the minimum and maximum connection limits that you define in Modeler.
> 
> John
> 
> On Wed, May 2, 2012 at 8:05 AM, Andrew Willerding
> <awillerding@itsurcom.com>wrote:
> 
>> On 05/02/2012 05:11 AM, Durchholz, Joachim wrote:
>> 
>>> I'd probably look up the Cayenne docs on connection pooling, and just
>>> make sure that everything is configured explicitly that the web container
>>> would do for you implicitly. BTW I've been working on a J2SE application
>>> for the last three years, and it's probably really a good idea to design
>>> the application around "requests" or "transactions". Transactions can fail
>>> due to transient errors, so you want them restartable, which means you need
>>> to wrap them in objects, and there you have your requests. (This pattern
>>> also sucks greatly because it isn't easy to pass results back to the
>>> caller. Essentially, you're doing the exactly same web service
>>> architecture, except it's running inside a single JVM.)
>>> 
>> I got the impression that there was some sort of connection pooling
>> built-in to Cayenne because in the Modeller there is a setting for minimum
>> and maximum connections.  Now I'm getting confused and perhaps I'm using
>> incorrect terminology.
>> 
>> In my mind there is the actual connection to the database as defined
>> during the creation of the DataContext.  In the application code I am
>> creating an ObjectContext based on the DataContext with a call to
>> DataContext.**createChildContext().  It is this ObjectContext where I can
>> create/delete manipulate the contents of the database.
>> 
>> But in a multi-threaded application do I need to create several
>> ObjectContexts or can one ObjectContext be shared among all the threads?
>> If the ObjectContext is sharable then do I need to synchronize access to
>> it?  If it needs to by synchronized then the "200th" thread will be in a
>> long line-up which is why I would see the need to create several pooled
>> ObjectContexts.  But then this takes be back to connection pooling as
>> defined in the Modeller.  If everything goes back through a single
>> connection then it's pointless to create and manage ObjectContexts as the
>> bottleneck may be "deeper" in the Cayenne library.
>> 
>> Help!  I getting trapped in my own recursive thoughts.
>> 
>> ;-)
>> 


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