.net - 为什么 OracleDataAdapter.Fill() 很慢？

Question

我正在使用一个非常复杂的查询从我们的一个计费数据库中检索一些数据。

我遇到了一个问题，当使用 SQL Developer 执行时，查询似乎很快完成，但在使用 OracleDataAdapter.Fill() 时似乎永远不会完成。方法。

我只尝试读取大约 1000 行，查询在 SQL Developer 中完成大约 20 秒。

是什么导致了如此巨大的性能差异？我有很多其他查询可以使用相同的功能快速运行。

这是我用来执行查询的代码:

using Oracle.DataAccess.Client;

...

public DataTable ExecuteExternalQuery(string connectionString, string providerName, string queryText)
{
    DbConnection connection = null;
    DbCommand selectCommand = null;
    DbDataAdapter adapter = null;

    switch (providerName)
    {
        case "System.Data.OracleClient":
        case "Oracle.DataAccess.Client":
            connection = new OracleConnection(connectionString);
            selectCommand = connection.CreateCommand();
            adapter = new OracleDataAdapter((OracleCommand)selectCommand);
            break;
        ...
    }

    DataTable table = null;
    try
    {
        connection.Open();

        selectCommand.CommandText = queryText;
        selectCommand.CommandTimeout = 300000;
        selectCommand.CommandType = CommandType.Text;

        table = new DataTable("result");
        table.Locale = CultureInfo.CurrentCulture;
        adapter.Fill(table);
    }
    finally
    {
        adapter.Dispose();

        if (connection.State != ConnectionState.Closed)
        {
            connection.Close();
        }
    }

    return table;
}

这是我正在使用的 SQL 的大纲:

with
  trouble_calls as
  (
    select
      work_order_number,
      account_number,
      date_entered
    from
      work_orders
    where
      date_entered >= sysdate - (15 + 31)  -- Use the index to limit the number of rows scanned
     and
      wo_status not in ('Cancelled')
     and
      wo_type = 'Trouble Call'
  )
select
  account_number,
  work_order_number,
  date_entered
from
  trouble_calls wo
where
  wo.icoms_date >= sysdate - 15
 and
  (
    select
      count(*)
    from
      trouble_calls repeat
    where
      wo.account_number = repeat.account_number
     and
      wo.work_order_number <> repeat.work_order_number
     and
      wo.date_entered - repeat.date_entered between 0 and 30
  ) >= 1

Answer 1

这段代码帮助了我，试试看:

using (OracleConnection conn = new OracleConnection())
{
     OracleCommand comm = new OracleCommand();
     comm.Connection = conn;
     comm.FetchSize = comm.FetchSize * 16;
     comm.CommandText = "select * from some_table";

     try
     {
          conn.Open();
          OracleDataAdapter adap = new OracleDataAdapter(comm);
          System.Data.DataTable dt = new System.Data.DataTable();
          adap.Fill(dt);
     }
     finally
     {
          conn.Close();
     }
}

技巧是一致的(尝试从 8 到 64 的值以找到最适合您的情况):

comm.FetchSize = comm.FetchSize * 16;

更新:

这是一个改进的代码:

OracleConnection myConnection = new OracleConnection(myConnectionString);
OracleCommand myCommand = new OracleCommand(mySelectQuery, myConnection);
myConnection.Open();
using (OracleDataReader reader = myCommand.ExecuteReader(CommandBehavior.CloseConnection))
{
    // here goes the trick
    // lets get 1000 rows on each round trip
    reader.FetchSize = reader.RowSize * 1000;

    while (reader.Read())
    {
        // reads the records normally
    }
}// close and dispose stuff here

来自 here