If keep_node_creation_backtrace, then whenever a new node is created, incremental will call Backtrace.get and store the result in the node. The backtrace will then appear in subsequent error messages when the node is pretty printed.
val set_keep_node_creation_backtrace : _t->bool -> unit
set_max_height_allowed t height sets the maximum allowed height of nodes. set_max_height_allowed raises if called during stabilization, or if height <
max_height_seen t.
num_active_observers returns (in constant time) the number of observers that have been created and not yet disallowed (either explicitly or via finalization).
constant-time stats
These are counters that are constant time to read, and that are automatically updated in the ordinary course.