如何修复“从池中获取连接之前已过超时时间”

Question

The following error seems to show every so often when loading up one of the pages on the site.

"Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached."

Based on what I found from searching around, it seems that the database connection isn't being closed properly and hence leaking. But I'm not too familiar with ASP.net, so would truly appreciate some guidance.

private void DisplayData()
    {
        SqlConnection objCon = new SqlConnection();
        objCon.ConnectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        objCon.Open();

        SqlCommand objCmd = new SqlCommand();
        objCmd.Connection = objCon;

        if (Request["Category"] == "some_cat")
        {
            objCmd.CommandText = "Select * From Community Where Category = N'some_cat' Order By Num Desc";
        }
        else if (Request["Category"] == "other_cat")
        {
            objCmd.CommandText = "Select * From Community Where Category = N'other_cat' Order By Num Desc";
        }
        else if (Request["Category"] == "Blog")
        {
            objCmd.CommandText = "Select * From Community Where Category = N'Blog' Order By Num Desc";
        }
        else if (Request["Category"] == "All")
        {
            objCmd.CommandText = "Select * From Community Where Category != N'Blog' Order By Num Desc";
        }


        objCmd.CommandType = CommandType.Text;

        SqlDataAdapter objDa = new SqlDataAdapter();
        objDa.SelectCommand = objCmd;

        DataSet objDs = new DataSet();

        objDa.Fill(objDs, "Community");

        this.ctlList.DataSource = objDs.Tables[0];
        this.ctlList.DataBind();

    objCon.Close();

    }

Answer 1

Your problem is possibly originated by the missing dispose of the connection object. A disposable object should be disposed (IE calling its Dispose method) to release all the unmanaged resources contained in the object. The using statement will make this easy because, even in case of exceptions, it calls the Dispose method for the object enclsed in its starting block.

A using statement is a simple way to write a try/finally block

SqlConnection con = new SqlConnection();
try
{

}
finally
{
    con.Dispose(); // And this will also close the connection
}

So your code could be changed to:

private void DisplayData()
{
    using(SqlConnection objCon = new SqlConnection())
    using(SqlCommand objCmd = new SqlCommand())
    {
         objCon.ConnectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        objCon.Open();

        objCmd.Connection = objCon;
        objCmd.CommandText = "Select * From Community Where Category = @cat Order By Num Desc";
        objCmd.Parameters.Add("@cat", SqlDbType.NVarChar).Value = Request["Category"].ToString();

        if (Request["Category"] == "All")
        {
           objCmd.CommandText = "Select * From Community Where Category != @cat Order By Num";
           objCmd.Parameters[0].Value = "Blog"    
        }
        SqlDataAdapter objDa = new SqlDataAdapter();
        objDa.SelectCommand = objCmd;
        DataSet objDs = new DataSet();
        objDa.Fill(objDs, "Community");
        this.ctlList.DataSource = objDs.Tables[0];
        this.ctlList.DataBind();
}

Of course, to remove the connection pool problem you should check all your code where you create an SqlConnection and implement the using block.