[Postgres-xl-developers] Postgres XL and Npgsql: Coordinator Exception

Jaaromy Zierse jzierse at ghostery.com
Thu Apr 9 09:59:28 PDT 2015


This seems to be a problem with Npgsql. We are successfully able to run
queries connecting via other methods. Is there something we need to
configure specifically for Npgsql?

On Wed, Apr 8, 2015 at 8:55 PM, Koichi Suzuki <koichi.dbms at gmail.com> wrote:

> Was the configuration successful?   You can check pgxc_node catalog to
> see your cluster configuration.   Also, you can raise the message
> level to have more detailed info on the exception.
>
> If you are checking that a datanode is running, you can issue select
> statement directly to a datanode, which should work.   Also, to check
> connectivity from coordinator to datanode, you can use "EXECUTE
> DIRECT" statement to issue read sql statement to a datanode.
>
> Regards;
> ---
> Koichi Suzuki
>
>
> 2015-04-09 11:49 GMT+09:00 Jaaromy Zierse <jzierse at ghostery.com>:
> > I updated the data node directly simply as a test, since inserting via
> the coordinator is throwing the exception. I simply wanted to verify that
> the issue wasn't something to do with a connection problem with the server
> or something similar.
> >
> >
> >> On Apr 8, 2015, at 8:43 PM, Koichi Suzuki <koichi.dbms at gmail.com>
> wrote:
> >>
> >> It is XL's specification that no direct updating operation is allowed
> >> to maintain data integrity within the cluster.   In other words,
> >> datanode is a backend element and is normally invisible from
> >> applications.
> >>
> >> Could you let me know the background that you are updating datanode
> directly?
> >>
> >> Regards;
> >> ---
> >> Koichi Suzuki
> >>
> >>
> >> 2015-04-09 8:25 GMT+09:00 Jaaromy Zierse <jzierse at ghostery.com>:
> >>> I am getting the following error when using Npgsql to execute any
> statement
> >>> against any of my Postgres XL coordinators:
> >>>
> >>> ERROR: XX000: Could not begin transaction on data node.
> >>>
> >>> Connecting via pgAdmin III and executing a query against the
> coordinators
> >>> successfully executes and distributes the data.
> >>>
> >>> Strangely, if I connect directly to the Datanodes using Npgsql, then
> the
> >>> statements execute successfully.
> >>>
> >>> Here is an example of the Npgsql code:
> >>>
> >>> using (var connection = new NpgsqlConnection(connectionString))
> >>> {
> >>>    connection.Open();
> >>>
> >>>    using (var command = connection.CreateCommand())
> >>>    {
> >>>        command.CommandText = @"SET TRANSACTION READ WRITE;
> >>>                                                        INSERT INTO
> test_table(
> >>>                                                        id, name)
> >>>                                                        VALUES (1,
> 'Rando');";
> >>>
> >>>        command.ExecuteNonQuery();
> >>>    }
> >>> }
> >>>
> >>>
> >>> Below is a description of our cluster configuration:
> >>>
> >>> Server: DEV-PGGTM
> >>> Postgres XL Components: GTM and GTM Proxy
> >>>
> >>> Server: DEV-PG1
> >>> Postgres XL Components: Coordinator 1 (Coord1) and Datanode1
> (Datanode1)
> >>>
> >>> Server: DEV-PG2
> >>> Postgres XL Components: Coordinator 2 (Coord2) and Datanode2
> (Datanode2)
> >>>
> >>> Server: DEV-PG1
> >>> Postgres XL Components: Coordinator 1 (Coord3) and Datanode3
> (Datanode3)
> >>>
> >>> All coordinators run on port 5432 and all datanodes run on port 15432.
> >>>
> >>> The GTM is using port 6666 and the GTM Proxy is using port 6668.
> >>>
> >>>
> >>> Thank you.
> >>>
> >>>
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> >>>
>



-- 

*Jaaromy Zierse*
Senior Software Engineer
O: 917.262.2530 | M: 801.722.5092 | E: jzierse at ghostery.com
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