On Mon, Dec 14, 2020 at 11:00 PM Fujii Masao <masao.fu...@oss.nttdata.com> wrote: > > One more point for the above scenario: if the user mapping is dropped > > in another session, then cache lookup for that entry in the > > postgres_fdw_get_connections() returns a null tuple which I plan to > > not throw an error, but just to skip in that case and continue. But if > > the user mapping is not dropped in another session but altered, then > > postgres_fdw_get_connections() still can show that in the output. > > Yes, so *if* we really want to return even connection invalidated by drop of > user mapping, the cached connection entry may need to store not only > user mapping id but also server id so that we can get the server name without > user mapping entry.
We can do that, but what happens if the foreign server itself get dropped with cascade option in another session, use case is as follows: 1) Run a foreign query in session 1 with server 1, user mapping 1 2) Try to drop foreign server 1, then we would not be allowed to do so because of dependency, if we use CASCADE, then the dependent user mapping 1 and foreign tables get dropped too. 3) Run the postgres_fdw_get_connections(), at the start of txn, the cached entry gets invalidated via pgfdw_inval_callback() and we try to use the stored server id of the invalid entry (for which the foreign server would have been dropped) and lookup in sys catalogues, so again a null tuple is returned. With Regards, Bharath Rupireddy. EnterpriseDB: http://www.enterprisedb.com
