Re: [HACKERS] 'Waiting on lock'

Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> How you figure that?

> Well I'm not clear exactly what's going on with the semaphores here. If it's
> possible for to be printing the messages only as a result of another backend
> unlocking the semaphore then making the PGSemaphoreUnlock conditional on
> log_lock_waits means you can't enable log_lock_waits after startup and get
> deterministic behaviour because whether you get messages will depend on which
> other backend happens to wake you up.

I don't see how you arrive at that conclusion. The message is printed
by the backend that is waiting for (or just obtained) a lock, dependent
on its own local setting of log_lock_waits, and not dependent on who
woke it up.

BTW, I just noticed that GUC allows deadlock_timeout to be set all the
way down to zero. This seems bad --- surely the minimum value should at
least be positive? As CVS HEAD stands, you're likely to get a lot of
spurious/useless log messages if you have log_lock_waits = true and
deadlock_timeout = 0. Do we care?

regards, tom lane