With multiple DocumentNodeStore instances in a cluster, the root document can become a bottleneck when many concurrent commits use it as a commit root.
The DocumentStore API currently requires that all operations that update documents immediately reflect all changes from other cluster nodes. Either when returning the before Document or implicitly via a subsequent find or query operation that may be served from the cache.
However, the DocumentNodeStore only needs to see external changes on the root node when it does a background read (or when it detects a collision). In almost all cases it would be fine with an update operation that does not immediately reflect external changes in the cache.