Finding out the size of subspace in foundationdb

we are using single fdb cluster for handling multiple tenants. Each tenant data, we are segregating with the subspace directory in foundationdb.

Now i would like to know, how much storage each tenant is using? Means what is the size of subspace for each tenant in fdb?

There is fdb_transaction_get_estimated_range_size_bytes which will use the histograms to give you an estimate. If you want to have something precise I am afraid that you have the query the whole range (or materialize this by doing your own book keeping).