Hi all, `FlatLedgerManager` is not useful at production and most of the production environment I knew don't use `FlatLedgerManager`. But the default value in the configuration is still setting to `FlatLedgerManager`, which doesn't sound right for the new users. so I think it is the time to raise the discussion of deprecating `FlatLedgerManager` and make `HierarchicalLedgerManager` as the default.
I created an issue for tracking this. Please comment if you see any problem of making `HierarchicalLedgerManager` as the default. https://github.com/apache/bookkeeper/issues/1101 - Sijie
