if a node R1 is in IS mode then it may be a possibility that some node below it is in exclusive
lock then how can we lock R1 in S mode since if I apply S on it that means I am
trying to lock every node below R1 in S mode but since some node below it is already
in exclusive lock so then how can I apply S lock on it .
since may be initially R1 was in IX mode but some other transaction came and applied
IS to it that means some node below R1 can be both in exclusive mode and in shared mode if R1 is
in IS mode so than how can a transaction come and lock R1 in shared mode i.e. why are IS and S locks
compatible ?
