OracleDataReader.Read方法的超时

Question

ODP.NET OracleCommand类具有CommandTimeout属性,可用于强制执行命令的超时.此属性似乎适用于CommandText是SQL语句的情况.示例代码用于说明此属性的实际应用.在代码的初始版本中,CommandTimeout设置为零 - 告诉ODP.NET不强制执行超时.

using System;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.Linq;
using System.Text;
using Oracle.DataAccess.Client;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            using (OracleConnection con = new OracleConnection("User ID=xxxx; Password=xxxx; Data Source=xxxx;"))
            using (OracleCommand cmd = new OracleCommand())
            {
                con.Open();                
                cmd.Connection = con;

                Console.WriteLine("Executing Query...");

                try
                {
                    cmd.CommandTimeout = 0;

                    // Data set SQL:
                    cmd.CommandText = "<some long running SQL statement>";
                    cmd.CommandType = System.Data.CommandType.Text;

                    Stopwatch watch1 = Stopwatch.StartNew();
                    OracleDataReader reader = cmd.ExecuteReader();
                    watch1.Stop();
                    Console.WriteLine("Query complete.  Execution time: {0} ms", watch1.ElapsedMilliseconds);

                    int counter = 0;
                    Stopwatch watch2 = Stopwatch.StartNew();
                    if (reader.Read()) counter++;
                    watch2.Stop();
                    Console.WriteLine("First record read: {0} ms", watch2.ElapsedMilliseconds);

                    Stopwatch watch3 = Stopwatch.StartNew();
                    while (reader.Read())
                    {
                        counter++;
                    }
                    watch3.Stop();
                    Console.WriteLine("Records 2..n read: {0} ms", watch3.ElapsedMilliseconds);
                    Console.WriteLine("Records read: {0}", counter);
                }
                catch (OracleException ex)
                {
                    Console.WriteLine("Exception was thrown: {0}", ex.Message);
                }

                Console.WriteLine("Press any key to continue...");
                Console.Read();
            }
        }
    }
}

上面代码的示例输出如下所示:

Executing Query...
Query complete.  Execution time: 8372 ms
First record read: 3 ms
Records 2..n read: 1222 ms
Records read: 20564
Press any key to continue...

如果我将CommandTimeout更改为3 ...

cmd.CommandTimeout = 3;

...然后运行相同的代码会产生以下输出:

Executing Query...
Exception was thrown: ORA-01013: user requested cancel of current operation
Press any key to continue...

调用返回引用游标的存储过程是另一回事.考虑下面的测试过程(纯粹用于测试目的):

PROCEDURE PROC_A(i_sql VARCHAR2, o_cur1 OUT SYS_REFCURSOR)
is
begin

    open o_cur1
    for
    i_sql;

END PROC_A;

下面的示例代码可用于调用存储过程.请注意,它将CommandTimeout设置为值3.

using System;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.Linq;
using System.Text;
using Oracle.DataAccess.Client;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            using (OracleConnection con = new OracleConnection("User ID=xxxx; Password=xxxx; Data Source=xxxx;"))
            using (OracleCommand cmd = new OracleCommand())
            {
                con.Open();                
                cmd.Connection = con;

                Console.WriteLine("Executing Query...");

                try
                {
                    cmd.CommandTimeout = 3;

                    string sql = "<some long running sql>";
                    cmd.CommandText = "PROC_A";
                    cmd.CommandType = System.Data.CommandType.StoredProcedure;
                    cmd.Parameters.Add(new OracleParameter("i_sql", OracleDbType.Varchar2) { Direction = ParameterDirection.Input, Value = sql });
                    cmd.Parameters.Add(new OracleParameter("o_cur1", OracleDbType.RefCursor) { Direction = ParameterDirection.Output });

                    Stopwatch watch1 = Stopwatch.StartNew();
                    OracleDataReader reader = cmd.ExecuteReader();
                    watch1.Stop();
                    Console.WriteLine("Query complete.  Execution time: {0} ms", watch1.ElapsedMilliseconds);

                    int counter = 0;
                    Stopwatch watch2 = Stopwatch.StartNew();
                    if (reader.Read()) counter++;
                    watch2.Stop();
                    Console.WriteLine("First record read: {0} ms", watch2.ElapsedMilliseconds);

                    Stopwatch watch3 = Stopwatch.StartNew();
                    while (reader.Read())
                    {
                        counter++;
                    }
                    watch3.Stop();
                    Console.WriteLine("Records 2..n read: {0} ms", watch3.ElapsedMilliseconds);
                    Console.WriteLine("Records read: {0}", counter);
                }
                catch (OracleException ex)
                {
                    Console.WriteLine("Exception was thrown: {0}", ex.Message);
                }

                Console.WriteLine("Press any key to continue...");
                Console.Read();
            }
        }
    }
}

上面代码的示例输出如下所示:

Executing Query...
Query complete.  Execution time: 34 ms
First record read: 8521 ms
Records 2..n read: 1014 ms
Records read: 20564
Press any key to continue...

请注意,执行时间非常快(34毫秒),并且未引发超时异常.我们在这里看到的性能是因为在第一次调用OracleDataReader.Read方法之前,不会执行ref游标的SQL语句.当第一次Read()调用从refcursor读取第一个记录时,将导致长时间运行的查询中的性能命中.

我已经说明的行为意味着OracleCommand.CommandTimeout属性不能用于取消与ref游标关联的长时间运行的查询.我不知道ODP.NET中的任何属性可以用来限制在这种情况下引用游标SQL的执行时间.任何人都有一些关于如何在一定时间后短路执行长时间运行的引用游标SQL语句的建议？

Answer 1

这是我最终采用的解决方案。它只是 OracleDataReader 类的扩展方法。该方法有一个超时值和一个回调函数作为参数。回调函数通常（如果不是总是）是 OracleCommand.Cancel。

namespace ConsoleApplication1
{
    public static class OracleDataReaderExtensions
    {
        public static bool Read(this OracleDataReader reader, int timeout, Action cancellationAction)
        {
            Task<bool> task = Task<bool>.Factory.StartNew(() => 
                {
                    try
                    {
                        return reader.Read();
                    }
                    catch (OracleException ex)
                    {
                        // When cancellationAction is called below, it will trigger 
                        // an ORA-01013 error in the Read call that is still executing.
                        // This exception can be ignored as we're handling the situation
                        // by throwing a TimeoutException.
                        if (ex.Number == 1013)
                        {
                            return false;
                        }
                        else
                        {
                            throw;
                        }
                    }
                });

            try
            {
                if (!task.Wait(timeout))
                {
                    // call the cancellation callback function (i.e. OracleCommand.Cancel())
                    cancellationAction();

                    // throw an exception to notify calling code that a timeout has occurred
                    throw new TimeoutException("The OracleDataReader.Read operation has timed-out.");
                }
                return task.Result;
            }
            catch (AggregateException ae)
            {
                throw ae.Flatten();
            }
        }
    }
}

下面是一个如何使用它的示例。

namespace ConsoleApplication1
{
    class Program
    {
        static string constring = "User ID=xxxx; Password=xxxx; Data Source=xxxx;";

        static void Main(string[] args)
        {
            using (OracleConnection con = new OracleConnection(constring))
            using (OracleCommand cmd = new OracleCommand())
            {
                cmd.Connection = con;
                con.Open();

                Console.WriteLine("Executing Query...");

                string sql = "<some long running sql>";
                cmd.CommandText = "PROC_A";
                cmd.CommandType = System.Data.CommandType.StoredProcedure;
                cmd.Parameters.Add(new OracleParameter("i_sql", OracleDbType.Varchar2) { Direction = ParameterDirection.Input, Value = sql });
                cmd.Parameters.Add(new OracleParameter("o_cur1", OracleDbType.RefCursor) { Direction = ParameterDirection.Output });

                try
                {
                    // execute command and get reader for ref cursor
                    OracleDataReader reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);

                    // read first record; this is where the ref cursor SQL gets evaluated
                    Console.WriteLine("Reading first record...");
                    if (reader.Read(3000, cmd.Cancel)) { }

                    // read remaining records
                    Console.WriteLine("Reading records 2 to N...");
                    while (reader.Read(3000, cmd.Cancel)) { }
                }
                catch (TimeoutException ex)
                {
                    Console.WriteLine("Exception: {0}", ex.Message);
                }

                Console.WriteLine("Press any key to continue...");
                Console.Read();
            }
        }
    }
}

这是输出的示例。

Executing Query...
Reading first record...
Exception: The OracleDataReader.Read operation has timed-out.
Press any key to continue...