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Date: Mon, 24 Apr 2006 12:34:40 +0200
From: "Stefan Guggisberg" <stefan.guggisberg@gmail.com>
To: dev@jackrabbit.apache.org
Subject: Re: Transactions and Recovery
In-Reply-To: <loom.20060421T113954-136@post.gmane.org>
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References: <loom.20060421T113954-136@post.gmane.org>

On 4/21/06, Lo=EFcP=E9ron <loic.peron@bigfoot.com> wrote:
> Hi,
>
> I intend to use Jackrabbit as a JCA-enabled JCR content repository in a J=
2EE
> application. I will have large blobs to store. I need distributed transac=
tional
> behaviour to ensure consisytency with other systems. I also need recovery
> insurance in case of failure. My blobs should be stored on a file system.
>
> Some searches on this list seem to indicate that Jackrabbit is _not_
> transactional when using a file system base persistence manager. Does Jac=
krabbit
> delegate transactionality to the database?

no, jackrabbit doesn't delegate transactionality to the database.

jackrabbit's transaction support requires that changes are stored
atomically on the persistence layer. see PersistenceManager#store(ChangeLog=
).

the jdbc-based pm's make use of db transactions to guarantee that changes a=
re
stored atomically.

file-system based pm's would need a transactional FileSystem to accomplish
this. there's currently no FileSystem implementation in jackrabbit supporti=
ng
transactions.

also note that if you're using a jdbc-based pm that's confgured to store bl=
obs
in the file system rather than in the database (i.e. externalBlobs=3Dtrue)
your setup is not fully 'transactional' for the same reasons as stated abov=
e.

>
> If I need to use a database to benefit from transactional behaviour, may =
I use
> Derby as a local database and store my large blogs (up to 10Gb) in it?

in general, yes. but you may want to do some research if derby supports
blobs of 10gb size... you would also have to tweak derby's schema.

>
> If I need to store my blobs externally to the database due to their size,=
 will
> the  file system based blob storage benefit from tansactional behaviour t=
oo?

no, see above.

cheers
stefan

>
> Last but not least, what is required to be sure my repository will always=
 be
> able to recover from a crash, particularly given my file system storage
> constraints?
>
> Thanks to all for your hard work.
>
>
>