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ADONET64 vertica driver returns empty DataTable on Select count(*)

Hi,

sometimes my ADONET64 vertica driver returns an empty DataTable, when I run a "Select count(*) from " a View.
The c# code is the following:

            VerticaCommand command = _dbConnection.CreateCommand();
            command.Connection = _dbConnection;

           command.CommandText = "SELECT COUNT(*) FROM View";

            // Create the DataAdapter
            VerticaDataAdapter adapter = new VerticaDataAdapter {SelectCommand = command};

            // Fill the DataTable
            DataTable result = new DataTable();
            adapter.Fill(result);

After adapter.Fill(result) result should be a data table with one row, but sometimes it is just empty.
Any idea? Is that a bug in the driver?
vertica and driver version is v10.0.1-6

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Best Answer

  • Accepted Answer

    I think we found the problem. We figured that we probably had parallel queries using a async methods running the queries.
    Thanks.

Answers

  • Jim_KnicelyJim_Knicely Administrator
    edited June 12

    Can you check to see if the query is reaching Vertica?

    To do that, query the SYSTEMS tables.

    Example...

    verticademos=> CREATE VIEW d_view AS SELECT * FROM dual;
    CREATE VIEW
    
    verticademos=> \! vsql -c "SELECT COUNT(*) FROM d_view;"
     COUNT
    -------
         1
    (1 row)
    
    verticademos=> SELECT user_name, transaction_id, statement_id, success FROM query_requests WHERE request = 'SELECT COUNT(*) FROM d_view;';z
    
     user_name |  transaction_id   | statement_id | success
    -----------+-------------------+--------------+---------
     dbadmin   | 45035996274039952 |            1 | t
    (1 row)
    
    verticademos=> SELECT session_id, transaction_id, statement_id, processed_row_count FROM query_profiles WHERE query = 'SELECT COUNT(*) FROM d_view;';
                  session_id              |  transaction_id   | statement_id | processed_row_count
    --------------------------------------+-------------------+--------------+---------------------
     erticademos_node0001-1145916:0x97e5a | 45035996274039952 |            1 |                   1
    (1 row)
    

    Are there times whene the SUCCESS flag is false?

    If so, take a peek at the DC_ERRORS Data Collector table for the related TRANSACTION_ID and STATEMENT_ID:

    SELECT log_message FROM dc_errors WHERE transaction_id = 45035996274039952 AND statement_id = 1;

  • Hi,

    yes, we checked and it seems that queries are not reaching Vertica and there are no queries with success = false.
    This errors seems to occur, when we query data sets where count = 0 and/or we have several queries in a milliseconds time interval.

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