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

Koichi Suzuki koichi.dbms at gmail.com
Wed Apr 8 19:55:32 PDT 2015


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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