Abstract: A distributed data store may maintain versioned hierarchical data structures. Different versions of a hierarchical data structure may be maintained consistent with a transaction log for the hierarchical data structure. When access requests directed to the hierarchical data structure are received, a version of the hierarchical data structure may be identified for processing an access request. For access requests with snapshot isolation, the identified version alone may be sufficient to consistently process the access request. For access requests with higher isolation requirements, such as serializable isolation, transactions based on the access request may be submitted to the transaction log so that access requests resulting in committed transactions may be allowed, whereas access requests resulting in conflicting transactions may be denied.