In mongodb lets say at time t0, I issue a query that reads subset S1 of all records U. This query takes 20 seconds to run i.e it runs till t0+20. At t0+5 a document update is issued which updates a document that is not in S1. Will both queries run concurrently or will there be waits due to locking ?

I tried to go through the mongodb documentation but I could not figure it out.