Use hash codes instead of sequence numbers for string indexes
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Key: JCR-2760
URL: https://issues.apache.org/jira/browse/JCR-2760
Project: Jackrabbit Content Repository
Issue Type: Improvement
Components: jackrabbit-core
Reporter: Jukka Zitting
Priority: Minor
We use index numbers instead of namespace URIs or other strings in many places.
The two-way mapping between namespace URIs and index numbers is by default
stored in the repository-global ns_idx.properties file, and the index numbers
are allocated using a linear sequence. The problem with this approach is that
two repositories will easily end up with different string index mappings, which
makes it practically impossible to make low-level copies of workspace content
across repositories.
The ultimate solution for this problem would be to store the namespace URIs
closer to the stored content, ideally as an implementation detail of a
persistence manager.
An easier short-term solution would be to decrease the chances of two
repositories having different string index mappings. A simple (and
backwards-compatible) way to do this is to use the hash code of a namespace URI
as the basis of allocating a new index number. Hash collisions are fairly
unlikely, and can be handled by incrementing the intial hash code until the
collision is avoided. In the common case of no collisions (with a uniform hash
function the chance of a collision is less than 1% even with tousands of
registered namespaces) this solution allows workspaces to be copied between
repositories without worrying about the namespace index mappings.
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