During recent review of the INCLUDE covering index patch, I pushed to formalize the slightly delicate assumptions that we make around how index_truncate_tuple() is called. It's natural to call index_truncate_tuple() during a page split, when a buffer lock is held. This is what we actually do in most cases.
It occurred to me that it would be nice to be able to Assert(!AnyBufferLockHeldByMe()) at a certain point within index_form_tuple(), to make sure that our assumptions hold. If index_truncate_tuple() (or any other function) ever called index_form_tuple(), and ended up actually performing table access with an exclusive buffer lock held, we'd at least be able to catch the bug when assertions are enabled. A function that lets code assert that no buffer locks are held, for the rare cases where external table access is required seems like good general infrastructure. Does this seem like a good idea? This could get pretty expensive if it was overused, even by the standards of what we expect from assertion-enabled builds, but we could make it optional if the overhead got out of hand. -- Peter Geoghegan
