Ceph » RADOS

Currently, a cls method can only access an object's data and metadata.
However, in some cases, it would be useful if a cls method could read from a remote object by calling another cls method.

For example, suppose the following use-case.

1. There is an object class that holds tabular data in row-oriented format.
2. The object class provides a SQL-like method to access the data, which returns the data output to the caller.
3. There is a large dataset consisting of many partitions, each of which is stored as an object and can be accessed via the SQL-like method.

Now, we create a new object class that holds tabular data in column-oriented format, which is prefered by analytical applications.
With our new feature, the new object class can have a new gather method that reads from a remote object by calling the SQL-like method.
We could covert the existing row-oriented dataset into the new columnd-oriented dataset by using the gather method and creating an object for each column.

This convertion could be done outside Ceph in a client.
However, we prefer to avoid sending data back and forth between client/storage and rather do this directly within storage.