Thread: Something broken around FDW connection close
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.
Adding to open items...
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. Best regards, Etsuro Fujita
At Fri, 31 Mar 2017 12:32:39 +0900, Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> wrote in <f14ace82-d77e-f1fd-e313-f07df2c10a1b@lab.ntt.co.jp> > On 2017/03/31 8:28, David Rowley wrote: .. > > 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 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) ... > 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. Agreed, this behavior is mentioned here. https://www.postgresql.org/docs/9.6/static/postgres-fdw.html#AEN182920 | table_name | | This option, which can be specified for a foreign table, gives | the table name to use for the foreign table on the remote | server. If this option is omitted, the foreign table's name is | used. regards, -- Kyotaro Horiguchi NTT Open Source Software Center