Re: Large objects and savepoints - Snapshot reference leak

Thanks Alvaro, that is good to know. At the moment we are stuck with
version 9.1.9 and have to stay there at least for Linux. But do I
understand correctly, that the warning can be ignored for the moment?

On Fri, 2014-01-31 at 15:15 -0300, Alvaro Herrera wrote:
> Andreas Lubensky wrote:
> > Hi,
> >
> > I'm trying to read/write large objects via libpq. I encapsulated the
> > operations in a transaction but I wanted to put a savepoint before doing
> > any operations, so I can do a rollback in case anything fails without
> > breaking the current transaction. Now, when sth. actually fails and the
> > transaction is rolled back to the savepoint, the next commit results in
> > a warning:
> > Snapshot reference leak: Snapshot 0xb5e4b0 still referenced
> > I'm not sure what to make of that. Can it be ignored? Is rolling back
> > large object operations not possible?
>
> What vresion are you running? I wonder if this can be attributed to a
> bug fixed by this commit:
>
> Author: Heikki Linnakangas <heikki(dot)linnakangas(at)iki(dot)fi>
> Branch: master [357f75213] 2013-09-30 12:53:14 +0300
> Branch: REL9_3_STABLE Release: REL9_3_1 [f609d0743] 2013-09-30 12:53:56 +0300
> Branch: REL9_2_STABLE Release: REL9_2_5 [fc7a38f32] 2013-09-30 12:54:37 +0300
> Branch: REL9_1_STABLE Release: REL9_1_10 [cd6c03b5c] 2013-09-30 12:55:57 +0300
> Branch: REL9_0_STABLE Release: REL9_0_14 [c5c87f065] 2013-09-30 12:58:51 +0300
> Branch: REL8_4_STABLE Release: REL8_4_18 [fef01d419] 2013-09-30 13:00:00 +0300
>
> Fix snapshot leak if lo_open called on non-existent object.
>
> lo_open registers the currently active snapshot, and checks if the
> large object exists after that. Normally, snapshots registered by lo_open
> are unregistered at end of transaction when the lo descriptor is closed, but
> if we error out before the lo descriptor is added to the list of open
> descriptors, it is leaked. Fix by moving the snapshot registration to after
> checking if the large object exists.
>
> Reported by Pavel Stehule. Backpatch to 8.4. The snapshot registration
> system was introduced in 8.4, so prior versions are not affected (and not
> supported, anyway).
>
> --
> Álvaro Herrera http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services
>
>

--
with best regards,

Andreas Lubensky

Software Engineer