On Mon, Jul 27, 2015 at 2:32 PM, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote: > David Rowley wrote: >> I've not looked into the feasibility of it, but if it were also possible to >> have a "waiting_for" column which would store the process ID of the process >> that's holding a lock that this process is waiting on, then it would be >> possible for some smart guy to write some code which draws beautiful >> graphs, perhaps in Pg Admin 4 of which processes are blocking other >> processes. I imagine this as a chart with an icon for each process. >> Processes waiting on locks being released would have an arrow pointing to >> their blocking process, if we clicked on that blocking process we could see >> the query that it's running and various other properties that are existing >> columns in pg_stat_activity. > > 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. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
