A number of task-related queries on multi-valued properties use the old-style NXQL syntax like nt:actors = 'foo' (which uses an EXISTS at the SQL level) instead of the more efficient nt:actors/* = 'foo' (which uses a JOIN).
These queries should be converted to the more efficient new style.
Many NXQL queries are translated to SQL queries using keyword EXISTS.
In big databases it can work slow, and it depends on planners.
It is recomended to use JOIN instead.
For instance in postgres, the "user_tasks" page providers is translated to:
The timing for this query is showed here http://explain.depesz.com/s/uEiL
and it takes about 10 seconds.
EXISTS can be easly converted to JOIN:
In this case, the query takes 500ms.
The problem is related to databases planners.