Which operations create a lock and when should I worry?

[shd2h]

You may find this list helpful:

List of lock rules in documentation

I agree. Here is a table detailing which commands take which type of lock. Shared locks allow any number of other shared locks to exist at the same time, and these commands typically only read or add data. Only one exclusive lock can exist at any time, and it must be the only lock. These commands typically delete information from the repository, or otherwise require it to not change at all while they work. tl;dr: Shared allows other shared stuff to run. Exclusive doesn’t allow anything else …

• Operations that need a shared/non-exclusive lock can run at the same time as other operations that need a shared lock.
• Operations that need an exclusive lock cannot run at the same time as any other operations.