On 7/27/15 1:46 PM, Robert Haas wrote:
On Mon, Jul 27, 2015 at 2:43 PM, Alvaro Herrera
<alvhe...@2ndquadrant.com> wrote:
Robert Haas wrote:
On Mon, Jul 27, 2015 at 2:32 PM, Alvaro Herrera
<alvhe...@2ndquadrant.com> wrote:
I think this is already possible, is it not? You just have to look for
an identically-identified pg_locks entry with granted=true. That gives
you a PID and vxid/xid. You can self-join pg_locks with that, and join
to pg_stat_activity.
I remember we discussed having a layer of system views on top of
pg_stat_activity and pg_locks, probably defined recursively, that would
show the full graph of waiters/lockers.
It isn't necessarily the case that A is waiting for a unique process
B. It could well be the case that A wants AccessExclusiveLock and
many processes hold a variety of other lock types.
Sure, but I don't think this makes it impossible to figure out who's
locking who. I think the only thing you need other than the data in
pg_locks is the conflicts table, which is well documented.
Oh, hmm, one thing missing is the ordering of the wait queue for each
locked object. If process A holds RowExclusive on some object, process
B wants ShareLock (stalled waiting) and process C wants AccessExclusive
(also stalled waiting), who of B and C is woken up first after A
releases the lock depends on order of arrival.
Agreed - it would be nice to expose that somehow.
+1. It's very common to want to know who's blocking who, and not at all
easy to do that today. We should at minimum have a canonical example of
how to do it, but something built in would be even better.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Data in Trouble? Get it in Treble! http://BlueTreble.com
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