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From "Felix Meschberger (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (JCR-3534) Add JackrabbitSession.getValueByContentId method
Date Thu, 18 Apr 2013 06:23:16 GMT

    [ https://issues.apache.org/jira/browse/JCR-3534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13634889#comment-13634889
] 

Felix Meschberger commented on JCR-3534:
----------------------------------------

Re. signed "message" or HMAC

I agree with Jukka: The user id cannot be part of this transaction because there is no reason
to assume that to be the same. Even if the "name" is the same the actual entity represented
by the name need not be the same. This is essentially the same issue that NFS is faced with
the numeric user and group IDs.

But: we also need a way to inject that value through some public API such as the ValueFactory
or some other means. Assuming RMI or Davex is not the  going to work because we have two separate
systems where the data is extracted through the JackrabbitValue.getContentIdentifier() (or
some new API) method, serialized in a custom way and then reinjected through some new API
(or the ValueFactory if that can differentiate between a "message" binary and a real binary
!).

Re. Future Proof

Angela is quite right: It is essential, that whatever mechanism we implement for Jackrabbit
2 should also be available for Oak.
                
> Add JackrabbitSession.getValueByContentId method
> ------------------------------------------------
>
>                 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
>         Attachments: 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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