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

Jaaromy Zierse jzierse at ghostery.com
Wed Apr 8 19:49:43 PDT 2015


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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