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From "Tommaso Teofili (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (JCR-3534) Efficient copying of binaries across repositories with the same data store
Date Tue, 07 May 2013 14:41:16 GMT

    [ https://issues.apache.org/jira/browse/JCR-3534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13650886#comment-13650886
] 

Tommaso Teofili commented on JCR-3534:
--------------------------------------

> Any key generation should come from the repository itself. Currently it's mixed - generating
is done by the client (needs to know the right format) and later reading & validating
is done by the repository in createValue(). It should all be done by the repository, the client
code should not have to know the format of the signature. I was thinking that we change the
JackrabbitValue#getContentIdentity() [0] to return the final secure/signed token format. Should
be possible to detect old and new IDs IMHO. This requires that other code (where?) that uses
the content identity can work with the new format as well.

generating a BinaryReferenceMessage has to be done with BinaryReferenceMessage(String contentIdentity,
String key, long referencedBinaryLength) which doesn't require any knowledge of signature
/ message format.
I'm -0.5 for changing JackrabbitValue#getContentIdentity(), IMHO that may be really confusing
as it wouldn't expose the content identity anymore but a message with other semantics.

> - BinaryReferenceMessage should go into jackrabbit-api instead of jackrabbit-jcr-commons
since it's a specific Jackrabbit API and jcr-commons is more about utilities around both JCR
API users and JCR implementors, which makes it hard to find actual jackrabbit specific features

if you'd say jackrabbit-core then it probably makes more sense, otherwise it seems to me this
is not "that" high level to justify its belonging to jackrabbit-api, in the end its main purpose
is to allow "efficient copying of binaries across repositories with the same datastore", which
seems to me best fit a core concept related to some specific deployments.

> BinaryReferenceMessage also implements getStream(), read() and getSize() by providing
the message token - IMHO that is misleading if it is used as special interface only. These
should probably return null. The repository itself would never return such a Binary itself.

that's basically for compatibility with existing code where you may now receive such an object
and you wouldn't expect that to return null.

                
> 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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