Re: [Objectbridge-developers] connection questions

[Thomas M. <tho...@ho...>]

Hi Steven,

Thanks for your interest!

"Melzer, Steven" wrote:
> 
> Hello, my name is Steven Melzer and I am new to both ObjectBridge and
> persistence in general.  I have been looking for a persistence solution for
> our web based database storage.  We are an Oracle shop using Weblogic as our
> application server.  I downloaded ObjectBridge and built a very simple
> example using MySQL on my local machine at home.  It worked well.  But I
> have several questions when it comes to integrating it with WebLogic:
> 
> 1) It seems that the ConnectionManager holds its own pool of connections.  I
> wish to use WebLogic's DataSource as a connection pool.  I can see how to
> change the source to do this, but i did not want to modify core code without
> some feedback.
> 

I think it won't be a big help to rewrite the StatementManager to use a
DataSource pool.
If you have a look at the source of
StatementManager::getStatementForClass(...) you will see that we have
one StatementsForClass instance per persistent class (or ClassDecriptor
to be exact).
each instance keeps for PreparedStatements for permanent reuse: 
- selectByPkStmt
- insertStmt
- updateStmt
- deleteStmt

To keep these statements "hot" implies to keep the underlying
connections permanently open. Thus a ConnectionPool would not be of any
use. That's why there is no Connection.close() anywhere.
(Maybe I should put it into some finalizers, but until now this produced
no problems.)
I chose this design to get a maximum performance by only preparing those
Statements once and resusing them later.

Of course you can easily change ConnectionManager and StatementsForClass
together to use your ConnectionPool. In fact OJB had such a
ConnectionPool at some earlier point in time.

> 2) The ConnectionManager is a singleton class holding connections.  However,
> I never see these connection being released anywhere.  I check
> StatementForClass and StatementManager, but I cannot find a
> connection.close().  If the connection is maintained in the
> ConnectionManager and never released, then the entire application in
> WebLogic will share the same connections.  If our app has hundreds of
> simultaneous users, then the single connection is going to be a major
> bottleneck.  This goes back to the first question above.
> 

In my eyes the bottleneck with the current design of OJB is the
PersistenceBrokerImpl itself.
If you have a look at PersistenBrokerImpl.beginTransaction() you will
easily see that it can only perform one Transaction at a time. And as it
is a singleton instance this will be the true bottleneck!

If you use the odmg implementation this bottleneck situation will be
reduced, as it opens broker transactions only for a  very short period
of time. But if you confront it with really heavy load it will od course
have the same problem...

The bad news: right now OJB does NOT scale! So you will need some load
testing whether it can be savely used in your environment or not.
I have been using OJB with IBM WebSphere with only 5-10 concurrent users
without specific problems!

The good news: I'm just finished with the 0.5 release which completed
the ODMG API. My next deliverable is a scalable distributed architecture
for OJB. This will of course take a while...

By the way: 
- are you planning to use EntityBeans. If so you might have a look at my
BMP sample code in package test.ojb.ejb!

- Are there any special reasons why don't you use WebLogics standard
persistence framework TopLink?

best regards,


Thomas Mahler 


> thanks in advance,
> steve
> 
> Steven Melzer
> E-Business Technology
> 813.351.2215
> ste...@pa...
> 
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