Re: Something broken around FDW connection close - Mailing list pgsql-hackers

On 2017/03/31 8:28, David Rowley wrote:

create table t (a int, b int);
insert into t1 select x/100,x/100 from  generate_series(1,100000) x;
create extension if not exists postgres_fdw;
create server test_server foreign data wrapper postgres_fdw options
(host 'localhost', port '5432', dbname 'postgres');
create foreign table ft_t (a int,b int) server test_server;
select 'create user mapping for current_user server test_server
options(user ''' || current_user || ''');';
\gexec
select count(*) from pg_stat_Activity; -- > 6
analyze ft_t;
ERROR:  could not connect to server "test_server"
DETAIL:  FATAL:  sorry, too many clients already
CONTEXT:  Remote SQL command: DECLARE c1 CURSOR FOR SELECT a, b FROM
public.ft_t
Remote SQL command: SELECT a, b FROM public.ft_t
Remote SQL command: SELECT a, b FROM public.ft_t
Remote SQL command: SELECT a, b FROM public.ft_t
(lots of these)

select count(*) from pg_stat_Activity; --> 105

I've not had a moment to check into what's going on.

IIUC, I think the cause would be that since the foreign table ft_t is considered to be still foreign on the foreign server, which is actually the same server, postgres_fdw recursively repeats the loopback access to ft_t.  (So, the same thing would happen for something like: select * from ft_t.)  If the analysis is right, ISTM that it's the user's fault.