Data sharing impact on locking

When you use block-level data sharing, the IRLM must obtain the concurrence of the sharing system before granting global locks.

Root locks are global locks, and dependent segment locks are not. When you use block-level data sharing, locks prevent the sharing systems from concurrently updating the same buffer. The buffer is locked before making the update, and the lock is held until after the buffer is written during commit processing. No buffer locks are obtained when a buffer is read.

If a Q command code is issued on any segment, the buffer is locked. This prevents the sharing system from updating the buffer until the Q command code lock is released.