The documentation for library(persistency) for the predicate db_sync/1 notes
update
As
reload, but use incremental loading if possible. This allows for two processes to examine the same database file, where one writes the database and the other periodically callsdb_sync(update)to follow the modified data.
In checking the source code at GitHub (ref) I can not find the code that implements db_sync(update).
I would like to experiment with two processes to examine the same database file but can not find any example code to follow, nor the code that implements update to understand it.