A Cloud Model Storage/Repository: The modelix model-server

API doc | Repository | buildfile | Artifacts: Nexus GitHub Packages

The model-server component provides a storage for models.

Bringing models to the cloud requires an alternative to the file system (and git) based storage of models. Modelix implements a data structure that allows replication between all MPS instances connected to the same model-server. It is very similar to the git storage format, but instead of files it stores nodes in its key-value data store.

Real-Time Collaboration and Operational Transformation

To support real-time collaboration, in addition to the snapshot of a version, the model-server also stores the operations that were applied on the previous version to produce the new version. Conflicts between concurrent modification are resolved using operational transformation (OT). The usually hard part of OT is to guarantee convergence, meaning that all clients end up with the same result independent of the order in which they receive changes. This problem becomes trivial, because versions are identified by a hash over all the content. Any divergence will result in a different hash which can easily be detected.

The remaining problem is what to do when a divergence is detected. From git we know that switching between versions is fast, because it only has to apply the difference between these versions. The same is true here: Fixing a divergence is as easy as switching to the correct version. If a client does not have any local changes it does not even need to apply the change operations itself - it can just switch to the new version. So in the rare case of a divergence fixing it is nothing special and is an operation that happens all the time.

MPS and the model-server

While this component is independent of MPS, it is possible to replicates the data of the MPS internal module repository into a running model-server. This can be achieved using the modelix MPS plugin: One can connect an MPS instances to a model-server, upload the current module repository, and keep it synchronized. This can also be a local MPS instance without a web editor - both options are supported at the same time.

Development

To reformat and add license header to all files run:

../gradlew spotlessApply

APIs

Valid keys are keys starting with the PROTECTED_PREFIX ($$$).

For details please refer to the OpenAPI documentation under doc/model-server.json.