Re: Retry Cached Remote Connections for postgres_fdw in case remote backend gets killed/goes away - Mailing list pgsql-hackers

From Bharath Rupireddy
Subject Re: Retry Cached Remote Connections for postgres_fdw in case remote backend gets killed/goes away
Date
Msg-id CALj2ACVOw5jDLdAEmfqEa3r-PMQYhu-8Z3MsbHP3w8aV97h2aw@mail.gmail.com
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In response to Re: Retry Cached Remote Connections for postgres_fdw in case remote backend gets killed/goes away  (Fujii Masao <masao.fujii@oss.nttdata.com>)
Responses Re: Retry Cached Remote Connections for postgres_fdw in case remote backend gets killed/goes away
List pgsql-hackers
On Fri, Sep 25, 2020 at 3:21 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>
> I think that we can simplify the code by merging the connection-retry
> code into them, like the attached very WIP patch (based on yours) does.
>

+1.

>
> +                       else
> +                               ereport(ERROR,
> +                                       (errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
> +                                        errmsg("could not connect to server \"%s\"",
> +                                                       server->servername),
> +                                        errdetail_internal("%s", pchomp(PQerrorMessage(entry->conn)))));
>
> The above is not necessary? If this error occurs, connect_pg_server()
> reports an error, before the above code is reached. Right?
>

Removed.

Thanks for the comments.

I think we need to have a volatile qualifier for need_reset_conn, because of the sigsetjmp.
Instead of "need_reset_conn", "retry_conn" would be more meaningful and also instead of goto label name "reset;", "retry:".
I changed "closing connection %p to reestablish connection" to  "closing connection %p to reestablish a new one"
I also adjusted the comments to be under the 80char limit.
I feel, when we are about to close an existing connection and reestablish a new connection, it will be good to have a debug3 message saying that we "could not connect to postgres_fdw connection %p"[1].

Attaching v5 patch that has the above changes. Both make check and make check-world regression tests passes. Please review.

[1] This would tell the user that we are not able to connect to the connection.
postgres=# SELECT * FROM foreign_tbl;
DEBUG:  starting remote transaction on connection 0x55ab0e416830
DEBUG:  could not connect to postgres_fdw connection 0x55ab0e416830
DEBUG:  closing connection 0x55ab0e416830 to reestablish a new one
DEBUG:  new postgres_fdw connection 0x55ab0e416830 for server "foreign_server" (user mapping oid 16407, userid 10)
DEBUG:  starting remote transaction on connection 0x55ab0e416830
DEBUG:  closing remote transaction on connection 0x55ab0e416830
 a1  | b1  
-----+-----
 100 | 200

Without the above message, it would look like we are starting remote txn, and closing connection without any reason.

postgres=# SELECT * FROM foreign_tbl;
DEBUG:  starting remote transaction on connection 0x55ab0e4c0d50
DEBUG:  closing connection 0x55ab0e4c0d50 to reestablish a new one
DEBUG:  new postgres_fdw connection 0x55ab0e4c0d50 for server "foreign_server" (user mapping oid 16389, userid 10)
DEBUG:  starting remote transaction on connection 0x55ab0e4c0d50
DEBUG:  closing remote transaction on connection 0x55ab0e4c0d50
 a1  | b1  
-----+-----
 100 | 200

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com
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