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From Marcel May <marcel....@consol.de>
Subject Re: Questions about TX in Jackrabbit, JTA and Spec compliance
Date Tue, 24 Jul 2007 13:58:35 GMT
Hi Dominique!

Dominique Pfister wrote:
> Hi Marcel,
>
> On 7/9/07, Marcel May <marcel.may@consol.de> wrote:
>> I have two questions about Jackrabbit and tx handling.
>>
>> 1) Using Jackrabbit deployed as resource adapter (JCA) and using a
>> BundlePersistenceManager, I wonder if it is XA compliant:
>>
>> The persistence manager BundleDbPersistenceManager invokes
>> setAutoCommit() and commit() on the db connection in the
>> store(ChangeLog) method.
>>
>> This is illegal for managed connections (JTA and XA), right?
>> So what is the right PM/FS for JCA when I want XA? Is it possible at
>> all?
>
> The JDBC connection Jackrabbit uses is not a "shared resource",
> managed by some external component, but opened/used/closed by
> Jackrabbit itself. Therefore, I don't consider this behaviour as being
> illegal in terms of JTA/XA. Please correct me, if I'm wrong.
>
If there's no JTA/XA support, the only szenario for deploying Jackrabbit as
a JCA Resource would be for sharing it across applications in the
application server (=>ok).

I thought you would use Jackrabbit JCA to get Jackrabbit participating
in a distributed transaction (XA).
It says XA is supported by Jackrabbit if the JCA adapter is used.

Quote from the jackrabbit site http://jackrabbit.apache.org/doc/deploy.html:
" This setup also allows to take advantage of the XA facilities of the
Application Server and could use the application servers single sign-on
mechanisms that are provided as part of the J2EE framework."

So here it is wrongly mentioned that Jackrabbit JCA brings you JTA/XA
support?

Jackrabbit JCA basically wraps Jackrabbit Core, but still all the Core
PersistenceManager and FileSystem implementations
are used. These, as you mentioned as well, use and manager their own
JDBC connections and therefore can never be JTA/XA compliant:

- JTA/XA requires using a (distributed) transaction manager
- Jackrabbit directly invokes setAutoCommit/commit/rollback without a
transaction manager (illegal in JTA/XA terms!)
- Jackrabbit  Workspace with a DB FileSystem and DB PersistenceManager
have two separate configured
   connections w/o a transaction manager.

Example:
- If Jackrabbit rolls back a TX directly on a connection, the
distributed transaction will not know about this.
- If the distributed TX is rolled back, Jackrabbit might already have
invoked con.commit() ... therefore no
  rollback is possible.

>> 2) I wonder if the current Jackrabbit impl. is specification conform.
>>    I see a conflict with the JCR spec, chapter 8.1 about TXs and JCR
>> implementations:
>>
>> "A compliant content repository may support transactions. If it does
>> so, it must adhere to the Java Transaction API (JTA) specification
>> (see http://java.sun.com/products/jta/index.html).
>> Whether a particular implementation supports transactions can be
>> determined by querying the repository descriptor table with
>> Repository.getDescriptor("OPTION_TRANSACTIONS_SUPPORTED")"
>>
>> The return value of
>> session.getRepository().getDescriptor("option.transactions.supported")
>> is true, but no JTA is used (again, look at the persistence manager
>> implementations like BundlePersistenceManager, where TX operations are
>> performed directly on the database connection instead handled by a
>> transaction manager).
>>
>
> I'm not sure if I get you there: should Jackrabbit return "false"
> because of your first argument above?
>
Yes.

Spec says a JCR impl can support TXs, and if it supports TXs it must
support JTA. Right?
Can some Spec expert on the mailing list comment on this?


The Jackrabbit impl. can not be transactional on workspace level if
internally a
database PersistenceManager and a databasse FileSystem each have their
own database connection:
An operation spawns the persistence manager (=pm) and the filesystem
(=fm), right?
If one part (fm/pm) succeeds  and is commited, the other part (fm/pm)
might fail and
therefore violate the ACID principle?
How do the two db connections of PM and FS work together?
This IMO can only be managed by  JTA/XA.

I understand transaction as on eg Workspace level, not PM or FS level.
> Kind regards
> Dominique

Dominique, thanks alot for your comments. I really would like to clarify
on this.

My understanding of Jackrabbit internals is not that great, but the
individual
connections in FS and PM for a Workspace confuse me as how a tx for two
connections is handled correctly.

And I'd really like to use Jackrabbit JCA with XA support, for which I
have these concerns.

Cheers, and thx a million -
Marcel

P.S.: I'd be willing to provide a documentation patch at the end of this
discussion :-)

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