Scaling the primary store is generally left to the primary store itself. Available options vary based on the selected backend.
MongoDB is the currently recommended backend for the primary store.
A single replica set should be able to handle most installations.
For cases where it is not, MongoDB provides transparent
sharding support with the use of
Replicante Core uses a pure-rust mongodb driver prototype.
A more stable driver has recently been release and upgrade will be planned in the future.
While this has not been a problem yet, some issues with performance and/or advanced setups may arise. If that is the case please report them.
MongoDB sharding works by dividing the data across different replica sets (shards). To know how data should be divided and what data is needed by each query, MongoDB needs a shard key for each collection.
The selection of a good shard key is critical to the performance of a sharded cluster and depends on the exact schema of the data stored in each collection.
Once a key is selected it is not possible (read: complex and expensive) to change the shard key of a collection.
As Replicante Core is at the beginning of its path, several features are likely to result in changes to the schema of the stored data, including to the optimal sharding key.
Installations that want to make use of sharded clusters should carefully consider what their upgrade paths will be if/when the sharding key changes.
If you do run a Replicante Core cluster and plan to use sharding we would be very pleased to know.