[pgpool-general: 1858] Re: weird error with postgres_fdw & pgpool

[Tatsuo Ishii]

Ok.

"postgres_fdw establishes a connection to a foreign server during the
first query that uses a foreign table associated with the foreign
server. This connection is kept and re-used for subsequent queries in
the same session."

This seems to support my theory. Unless there's some way for pgpool to
know the connection is from postgres_fdw, there's no way to avoid the
client_idle_limit problem. The only workaround is set
client_idle_limit to 0. It would be nice if postgres_fdw periodically
sends something to pgpool to prevent pgpool from thinking the client
is idle.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

> I don't know any more than is documented here:
> http://www.postgresql.org/docs/devel/static/postgres-fdw.html
> 
> If there's something specific that you'd like me to change or test, let me know.
> 
> thanks
> 
> On Thu, Jun 20, 2013 at 8:02 AM, Tatsuo Ishii <ishii at postgresql.org> wrote:
>> No. Because I'm not familiar with postgres_fdw, I just wanted to make
>> sure what the cause of the problem is. I cannot promise I can solve
>> your problem, but I'm sure without knowing the cause, it's absolutely
>> impossible to solve the problem.
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese: http://www.sraoss.co.jp
>>
>>> I'm not sure that I understand the question. Are you asking me to set
>>> client_idle_limit to 0?
>>>
>>> On Wed, Jun 19, 2013 at 6:15 PM, Tatsuo Ishii <ishii at postgresql.org> wrote:
>>>> Lonni,
>>>>
>>>> Is it possible for postgres_fdw to create a persistent connection from
>>>> db11 to db12 for certain pupose(maybe connection pooling)? If so, the
>>>> connection will be treated as a normal conection from client by pgpool
>>>> and client_idle_limit will be applied.
>>>> --
>>>> Tatsuo Ishii
>>>> SRA OSS, Inc. Japan
>>>> English: http://www.sraoss.co.jp/index_en.php
>>>> Japanese: http://www.sraoss.co.jp
>>>>
>>>>> I'm in the process of testing out a beta of postgres-9.3 using
>>>>> pgpool-3.2.4 and the (new) postgres_fdw.   I have two different
>>>>> postgres-9.3 servers setup (db10 & db11), and pgpool is setup (db12)
>>>>> pointing to one of them (db10).  I can connect with psql to both
>>>>> servers directly, and also via pgpool, with no problems.  My intent
>>>>> was to be able to run SQL queries while logged into db11 through
>>>>> pgpool on db12 to the server on db10, using a postgres_fdw.
>>>>>
>>>>> I setup the postgres_fdw server:
>>>>> CREATE SERVER db10 FOREIGN DATA WRAPPER postgres_fdw OPTIONS (host
>>>>> 'db12', dbname 'nightly', port '9999');
>>>>> CREATE USER MAPPING FOR lfriedman SERVER db10 OPTIONS (user 'lfriedman');
>>>>> CREATE FOREIGN TABLE nppsmoke (id bigint NOT NULL, date_created
>>>>> timestamp without time zone not null default now(), last_update
>>>>> timestamp without time zone not null default now(), build_type text
>>>>> NOT NULL,current_status text NOT NULL, info text NOT NULL, cudacode
>>>>> text NOT NULL, gpu text NOT NULL, subtest text NOT NULL, os text NOT
>>>>> NULL, osversion text NOT NULL, arch text NOT NULL, cl integer NOT
>>>>> NULL, dispvers text NOT NULL, branch text NOT NULL, pass integer,fail
>>>>> integer, oldfail integer, newfail integer, failureslog text, totdriver
>>>>> boolean NOT NULL default 'true',ddcl integer NOT NULL, buildid
>>>>> integer, testdcmd text NOT NULL, pclog text, filtercount integer,
>>>>> filterlog text, error integer) SERVER db10 ;
>>>>>
>>>>> After which, I verified that I could issue SQL queries from inside
>>>>> psql while connected to db11, against the foreign table, nppsmoke that
>>>>> was created above:
>>>>> #########
>>>>> nightly=# select last_update from nppsmoke where id='86901' ;
>>>>>      last_update
>>>>> ---------------------
>>>>>  2013-06-12 12:53:23
>>>>> (1 row)
>>>>> #########
>>>>>
>>>>> However, I'm seeing some strange errors when my psql session exceeds
>>>>> the pgpool client_idle_limit:
>>>>> #######
>>>>> nightly=# select last_update from nppsmoke where id='86901' ;
>>>>> ERROR:  connection terminated due to client idle limit reached
>>>>> CONTEXT:  Remote SQL command: START TRANSACTION ISOLATION LEVEL REPEATABLE READ
>>>>> nightly=# select last_update from nppsmoke where id='86901' ;
>>>>> ERROR:  unknown error
>>>>> CONTEXT:  Remote SQL command: START TRANSACTION ISOLATION LEVEL REPEATABLE READ
>>>>> ########
>>>>>
>>>>> And the only way that I've found to run the SQL queries against the
>>>>> foreign table is to exit psql and connect again from scratch.  This is
>>>>> definitely different behavior than I experience for local tables.  For
>>>>> queries issued after the client_idle_limit, I always see:
>>>>> #####
>>>>> ERROR:  connection terminated due to client idle limit reached
>>>>> ERROR:  connection terminated due to client idle limit reached
>>>>> The connection to the server was lost. Attempting reset: Succeeded.
>>>>> #####
>>>>>
>>>>> after which I can re-run the query without exiting & reconnecting with psql.
>>>>>
>>>>> This seems like a bug to me, as I'd expect the behavior to be
>>>>> consistent regardless of what is on the remote end.  Thoughts?
> 
> 
> 
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> L. Friedman                                    netllama at gmail.com
> LlamaLand                       https://netllama.linux-sxs.org