Fix memory leakage in postgres_fdw's DirectModify code path. postgres_fdw tries to use PG_TRY blocks to ensure that it will eventually free the PGresult created by the remote modify command. However, it's fundamentally impossible for this scheme to work reliably when there's RETURNING data, because the query could fail in between invocations of postgres_fdw's DirectModify methods. There is at least one instance of exactly this situation in the regression tests, and the ensuing session-lifespan leak is visible under Valgrind.
We can improve matters by using a memory context reset callback attached to the ExecutorState context. That ensures that the PGresult will be freed when the ExecutorState context is torn down, even if control never reaches postgresEndDirectModify. I have little faith that there aren't other potential PGresult leakages in the backend modules that use libpq. So I think it'd be a good idea to apply this concept universally by creating infrastructure that attaches a reset callback to every PGresult generated in the backend. However, that seems too invasive for v18 at this point, let alone the back branches. So for the moment, apply this narrow fix that just makes DirectModify safe. I have a patch in the queue for the more general idea, but it will have to wait for v19. Author: Tom Lane <t...@sss.pgh.pa.us> Reviewed-by: Matheus Alcantara <matheusssil...@gmail.com> Discussion: https://postgr.es/m/2976982.1748049...@sss.pgh.pa.us Backpatch-through: 13 Branch ------ REL_16_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/2b92dc4eeb51a1b66641718e072b96b63659448c Modified Files -------------- contrib/postgres_fdw/postgres_fdw.c | 62 +++++++++++++++++++++---------------- 1 file changed, 35 insertions(+), 27 deletions(-)
