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From "Alexander Klimetschek (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (JCR-3534) Efficient copying of binaries across repositories with the same data store
Date Fri, 10 May 2013 07:41:17 GMT

    [ https://issues.apache.org/jira/browse/JCR-3534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13653621#comment-13653621
] 

Alexander Klimetschek commented on JCR-3534:
--------------------------------------------

The DataStore could generate this shared secret the first time it is started (i.e. no secret
present), store it in a file in the root folder in case of the FileDataStore, and then every
shared usage will have access to it anyway. Then this secret can be a secure long random string.

Implementation wise, AbstractDataStore would remove setSecret(), and add a getSecret(), which
it implements returning null - which means no reference binaries are supported here (i.e.
the DataIdentifier would get a null reference). Then DataStore implementations would override
the getSecret() method, which would look for the secret, and id not present, create it. AbstractDataStore
should provide a generateSecret() method to use. The FileDataStore would then define the name
and location of the file. Something like "secret" in the root folder of the storage should
work - afaics it cannot conflict with normal entries, since they are always in "hash" subdirectories.

For the DbDataStore it could be an special named entry that cannot collide with binaries.
For the MultiDataStore I don't know.
                
> 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-3534.4.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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