如何对 SQL Server 运行多个查询？

Question

I have read and implemented several different versions of Microsofts suggested methods for querying a SQL Server database. In all that I have read, each query is surrounded by a using statement, eg In some method DoQuery :

List<List<string>> DoQuery(string cStr, string query)  
{
    using(SqlConnection c = new SqlConnection(cStr)) 
    {
        c.Open();

        using(SqlCommand cmd = new SqlCommand(queryStr, c)) 
        {
            using(SqlDataReader reader = cmd.ExecuteReader()) 
            {
                while (reader.Read() ) 
                {
                     ...
                     //read columns and put into list to return
                }

           // close all of the using blocks
           }
        }
    }

    // return the list of rows containing the list of column values.
}

I need to run this code several hundreds of times for different query strings against the same database. It seems that creating a new connection each time would be inefficient and dropping it each time wasteful.

How should I structure this so that it is efficient? When I tried not using a using block and passing the connection into the DoQuery method, I got messages about the connection had not been closed. If I closed it after the query, then I got messages about it wasn't open.

I'm also trying to improve this because I keep getting somewhat random

IOException: Unable to read data from the transport connection: Operation on non-blocking socket would block.

I'm the only user of the database at this time and I'm not doing anything in multiple threads or async, etc. Just looping through query strings and running DoQuery on them.

Could my structure be part of that problem, ie not releasing the resources fast enough and thereby seeing the connection blocked?

I'm stuck here on efficiency and this blocking problem. Thanks in advance.

Answer 1

As it turns out, the query structure was fine and the queries were fine. The problem was that I had an 'order by X desc' on each query and that column was not indexed. This caused a full table scan to order the rows even if only returning 2. The table has about 3 million rows and I thought it could handle that better than it does. It timed out with 360 second connection timeout! I indexed the column and no more 'blocking' nonsense, which BTW, is a horrible message to return when it was actually a timeout. The queries now run fine if I index every column that appears in a where clause.