On Tue, Mar 10, 2015 at 11:54:23AM -0400, Tom Lane wrote: > Denys Rtveliashvili <r...@icloud.com> writes: > > My function neeeds to call a third-party library which would create a state > > and then that state should be kept for the duration of the current query. > > The library can deallocate that state in a correct way. > > > I understand that fn_extra is normally used for this and usually the state > > is created in a memory context which is deallocated at the end of the > > query. So normally it is not an issue. However, I cannot make that library > > use PostgreSQL utilities for memory management. > > > I am afraid that for long-running sessions it may cause serious memory > > leaks if they do not deallocate state correctly and in a timely manner. > > > Is there a mechanism for adding a finalizer hook which would be called and > > passed that pointer after the query is complete? Or perhaps there is > > another mechanism? I looked in the documentation and in the source but I do > > not see it mentioned. > > In HEAD, you could use a memory context reset callback for this purpose. > > I don't believe there's any fully satisfactory solution in the released > branches; the closest you could get is an ExprContext callback, which > has the fatal-for-this-purpose defect that it's only called on successful > query completion, not if an error occurs.
RegisterSubXactCallback() is an established tool for addressing this scenario in released branches. See how plpgsql and postgres_fdw use these xact callbacks to explicitly release special resources. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
