Advisory lock grant order

[Yossi Cohen]

Hi,

If I request an advisory lock (pg_advisory_lock) with the same key from
several sessions; will the lock be granted in the same order as it was
requested?
I.e. if for example:

session 1: select pg_advisory_lock(1); -- acquires the lock
then
session 2: select pg_advisory_lock(1); -- blocks waiting for the lock
then
session 3: select pg_advisory_lock(1); -- blocks waiting for the lock

then
session 1: select pg_advisory_unlock(1); -- releases the lock

Is it guaranteed that now session 2 will be granted the lock because it
requested the lock before session 3?

Thanks,
Yossi

[Tom Lane]

Post by Yossi Cohen
If I request an advisory lock (pg_advisory_lock) with the same key from
several sessions; will the lock be granted in the same order as it was
requested?

Usually. IIRC, the lock code will grant locks out-of-order if a deadlock
would result without it. There might be some other exceptions but I
don't recall any.

regards, tom lane