On Tue, Apr 5, 2016 at 1:10 PM, Simon Riggs <si...@2ndquadrant.com> wrote:
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> If a lock is successfully obtained on one table, but not on all tables, it >> releases that lock and will retry to get them as a group in the future. >> Since inheritance acts as a group of tables (top + recursive cascade to >> children), this implementation is necessary even if only a single table is >> specified in the command. >> > > I'd prefer to see this as a lock wait mode where it sits in the normal > lock queue BUT other lock requestors are allowed to queue jump past it. > That should be just a few lines changed in the lock conflict checker and > some sleight of hand in the lock queue code. > > That way we avoid the busy-wait loop and multiple DEFERRABLE lock waiters > queue up normally. > Yeah, that would be better. I can see how to handle a single structure in that way but I'm not at all certain how to handle multiple tables and inheritance is multiple tables even with a single command. X1 inherits from X There is a long-running task on X1. Someone requests LOCK TABLE X IN ACCESS EXCLUSIVE MODE WAIT PATIENTLY. Internally this also grabs X1. The lock on X might be granted immediately and now blocks all other access to that table. There would need be a Locking Group kind of thing so various LockTags are treated as a single entity to grant them simultaneously. That seems pretty invasive; at least I don't see anything like that today.
