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From "Marcel Reutegger (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (JCR-3534) Efficient copying of binaries across repositories with the same data store
Date Wed, 08 May 2013 07:07:16 GMT

    [ https://issues.apache.org/jira/browse/JCR-3534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13651672#comment-13651672
] 

Marcel Reutegger commented on JCR-3534:
---------------------------------------

I'd rename the BinaryReferenceMessage to ReferenceBinary. The data inside the ReferenceBinary
can be a message, but other than that the class is primarily a Binary and not a message.

More important however, is to make the API as small as possible. Right now, we have BinaryReferenceMessage
with many public methods. I think it would be much better to only have a few methods. I like
Jukka's suggestion earlier to create an abstract ReferenceBinary class without a direct dependency
to the message or reference internals. The message or reference inside the ReferenceBinary
could be an opaque String, which can easily be serialized and deserialized through various
protocols. The use of a HMAC then becomes an implementation detail.

The remaining question is how to get a ReferenceBinary from a Repository. I think this has
to go into the API (just like the ReferenceBinary). I'd probably add it to the existing JackrabbitValue
interface and add a method {{getReferenceBinary()}}. 
                
> Efficient copying of binaries across repositories with the same data store
> --------------------------------------------------------------------------
>
>                 Key: JCR-3534
>                 URL: https://issues.apache.org/jira/browse/JCR-3534
>             Project: Jackrabbit Content Repository
>          Issue Type: New Feature
>          Components: jackrabbit-api, jackrabbit-core
>    Affects Versions: 2.6
>            Reporter: Felix Meschberger
>            Assignee: Tommaso Teofili
>         Attachments: JCR-3534.2.patch, JCR-3534.3.patch, JCR-3534.patch, JCR-3534.patch
>
>
> we have a couple of use cases, where we would like to leverage the global data store
to prevent sending around and copying around large binary data unnecessarily: We have two
separate Jackrabbit instances configured to use the same DataStore (for the sake of this discussion
assume we have the problems of concurrent access and garbage collection under control). When
sending content from one instance to the other instance we don't want to send potentially
large binary data (e.g. video files) if not needed.
> The idea is for the sender to just send the content identity from JackrabbitValue.getContentIdentity().
The receiver would then check whether the such content already exists and would reuse if so:
> String ci = contentIdentity_from_sender;
> try {
>     Value v = session.getValueByContentIdentity(ci);
>     Property p = targetNode.setProperty(propName, v);
> } catch (ItemNotFoundException ie) {
>     // unknown or invalid content Identity
> } catch (RepositoryException re) {
>     // some other exception
> }
> Thus the proposed JackrabbitSession.getValueByContentIdentity(String) method would allow
for round tripping the JackrabbitValue.getContentIdentity() preventing superfluous binary
data copying and moving. 
> See also the dev@ thread http://jackrabbit.markmail.org/thread/gedk5jsrp6offkhi

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