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From "Eric Samson" <e...@xcalia.com>
Subject RE: multiple databases one PM/TX
Date Tue, 30 Oct 2007 12:24:28 GMT
Hey Matthew,

See my comments inline.


....: Eric Samson, Founder & CTO, xcalia

Service your Data!

De : Matthew Adams [mailto:matthew@matthewadams.org] 
Envoyé : lundi 29 octobre 2007 20:25
À : Eric Samson
Cc : Erik Bengtson; jdo-dev@db.apache.org; jdo-experts-ext@sun.com
Objet : Re: multiple databases one PM/TX


Hi all,


I like that JDO allows implementations to support this, and I do feel that this could be a
differentiator from JPA.  The things that come to my mind are the following:


* this should be an optional feature so that we don't slow down implementations from being

* we should examine the proposed JDO 2.1 metadata formats to ensure that it can support but
not require multiple data sources

[Eric Samson] Agreed.


* we need to examine the impact of configuring multiple data sources on the API (i.e., new
method JDOHelper.getPersistenceManagerFactory(String... names), PersistenceManager#getDataStoreConnection()
& JDOConnection#getNativeConnection?)

[Eric Samson] IMHO, this is more for the sake of completion rather than a real need, but why


* configuration of JTA and the coordination of transactions across all data sources

[Eric Samson] Do you want to configure distributed transactions or do you want the implementation
to decide how to (transparently ?) manage them? BTW: what kind of configuration do you have
in mind? Is that JTA only? What about WS-*? Or a mix of them? Or something else?


* this would slow down work on 2.1 -- can we add in another maintenance release?

[Eric Samson] Yes, should be later in time.




On Oct 29, 2007, at 10:05 AM, Eric Samson wrote:

Hello Erik,


Once again you start an important topic here! :-)


We also are working on a multi-data sources PMF.


I think the name "resource" could be confusing (I tend to prefer "data source").


Maybe the data source properties should be defined elsewhere (as you can have quite complex
configurations when you want to access non-relational data stores)?


Best Regards,

....: Eric Samson, Founder & CTO, Xcalia

Service your Data!


-----Message d'origine-----
De : Erik Bengtson [mailto:erik@jpox.org] 
Envoyé : vendredi 26 octobre 2007 15:49
À : jdo-dev@db.apache.org; jdo-experts-ext@sun.com
Objet : multiple databases one PM/TX


In JPOX we are implementing the access to multiple datastores within a single

PM/TX. If not too late, I'm wonder if you like to hear a proposal to

standardize the configuration of the "jdoconfig" and jdo metadata to be able to

handle this scenario. It may sound overkill, but IMO is a major advance over



To introduce the subject, the goal is to handle persistence in multiple

databases (e.g. derby, oracle, DB4O, Versant, XML) within a single JDO

transaction/ single PM. From the user point of view, there are two items that

must be configured, jdo metadata, jdo configuration, in which would be part of

this proposal, so I show below an example of the configurations:


/jdoconfig/ sequence unbounded PMF

/jdoconfig/ sequence unbounded Resource








/Resource/Connection Settings/

/Resource/Connection Settings/@ConnectionFactoryName

/Resource/Connection Settings/@ConnectionClientID

/Resource/Connection Settings/@ReadOnly

/Resource/Connection Settings/@...







ConnectionClientID is the identifier for the connection. Some databases such as

Oracle use this to identify the end user (not the connection user).

ConnectionClientID would accept the values:


1 - CredentialMapping - the CredentialMapping takes the principal of the running

application and sets it as client id - eg. ConnectionClientID=CredentialMapping

2 - Identity - the client id is taken from the id right after the Identity word

- eg. ConnectionClientID=Identity:MyUser




ReadOnly (accepts true, false) will block write operations to this connection




Two options:


1 - LastLoggingResource - If the resource is non XA, push down this resource in

commit order.

2 - Emulated - Emulates non XA protocol. Heuristics errors could happen






<pmf name="snowdog" default-resource="Oracle">



<resource name="ERP">

<connection connectionfactoryname="BSCS_Hot"/>



<resource name="PeopleSoft">

<connection connectionfactoryname="PS_Onyx"/>



<resource name="Oracle">

<connection connectionfactoryname="ORA_Vinci"


<transaction two-phase-commit="LLR" timeout="30"/>



<resource name="Xml">

<connection readonly="true"/>


<jpox:xml file="file:/usr/home/myxml.xml <file:///\\usr\home\myxml.xml> "/>









<class name="Invoice" resource="ERP"/>

<class name="ClassData"/> <!-- uses default-resource -->

<class name="Person" resource="PeopleSoft"/>

<class name="ReferenceData" resource="Xml"/>







Quoting Michelle Caisse <Michelle.Caisse@sun.com>:


> Hi,


> We will have our regular meeting Friday, October 26 at 9 am PDT to

> discuss JDO TCK issues and status.


> Dial-in numbers are:

> 866 230-6968   294-0479#

> International: +1 865 544-7856


> Agenda:


> 1. Subquery spec update

> 2. Other issues


> Action Items from weeks past:


> [Oct 12 2007] AI Michael take a look at subquery tck tests.

> https://issues.apache.org/jira/browse/JDO-446


> [Sep 14 2007] AI Matthew provide examples for jdoconfig.xml.


> [June 22 2007] AI Craig discuss svn:eol-style on email.


> [June 22 2007] AI Craig write a proposal on annotation overrides for

> the expert group.


> [May 25 2007]  AI everyone Download the Grails demo from grails.org  and

> check it out. Also look at Grails/Groovy ExpandoMetaClass that  has the

> magic to avoid reflection and enhancement.


> [May 25 2007] AI Matthew Adams prepare a proposal with just the  basics

> of schema synchronization with jdo and orm metadata.


> [May 18 2007] AI Craig update http://wiki.apache.org/jdo/

> CurrentDevelopment wiki page


> [Apr 27 2007] AI Craig review Query API and send email to experts.


> [Apr 27 2007] AI Erik file a JIRA regarding JPA style transactions  and

> attach his discussion document to it.


> [Mar 9 2007] AI Craig: Update the spec to require that the key of the

> listener is the class name of the listener, for consistency with

> proposed xml..


> [Mar 2 2007] AI Craig: update the JDOHelper class to include a string

> constant "META-INF/jdo.xml" and a new method

> getPersistenceManagerFactory taking no arguments.


> [Aug 11 2006] AI Craig propose some semantics for behavior if user

> tries to add to a list where the ordering element is incorrect.


> [Jul 14 2006] AI: Erik document 220 annotations that don't have a

> corresponding JDO concept.


> [Jun 23 2006]  AI  Martin look at what Hibernate and TopLink support

> for Enum types. In progress.


> [Apr 14 2006] AI Craig: update the roadmap for JDO. In progress.


> [Nov 4 2005] AI Martin: Update Martin's wiki with discusion of JDK   1.5

> issues. In progress


> [Sep 2 2005] AI: To recruit members, update the web site. Articles  on

> TheServerSide directing attention to the site. T-shirts, logo.    AI:

> Craig write a ServerSide article.


> -- Michelle


> >






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